It's no secret that you need to have good footwear for your mission. Your feet are your main method of travel, and even something like standing on the range for a day can cause fatigue if your feet aren't properly cared for.
The foot has 28 bones, and has an extremely complex bone structure relative to the other parts of your body. Man was originally fighting in fur or sandals, and then eventually we learned how to make more protective footwear. The problem with most modern footwear is that it goes against how your feet naturally want to move. Lace placement and tightness, boot height, insoles, waterproof vs non waterproof, and material can all make or break a boot.
Lacing your boots properly, and how your bootlace eyelets are set up will determine how your boots work with your blood flow and the top of your foot.
The old Vietnam era jungle boots have laces that start halfway up your foot. Which means the main point of strain on your boot is right in the middle of the foot, at a point that doesn't flex.
Since your laces are the main method of securing the boot to your foot, they should play well with the natural anatomy and mechanics of your foot. Putting a pressure point right in the top of your foot bone won't lend to working very well long term, whether it's rucking or running.
The Danner Reckoning, which is a modern day military boot, have the cross lace right above the main joints in your toes. This causes much less stress over the top of your foot, and will be more comfortable over a longer amount of time.
Does this mean that you will automatically be unbearably uncomfortable if your laces start halfway up your foot? No. But proper care of your feet will give you less issues over a longer amount of time.
How tight you lace your boots will also give you varying results. Many people will keep the bottom laces around their foot looser, and then the higher laces by their ankle tight. This can help provide support and give your toes room to spread as you walk, but tightening the laces too much up top can cut off circulation to your foot, and this can be detrimental over long periods of time or in the winter.
Finding the middle ground between snug fit to reduce blisters from friction, and loose fit to provide healthy movement and blood flow is something everybody needs to figure out. When boots are made, they are styled around a certain foot. If this foot is similar to your foot, then the boots from that company will fit well. If the model foot is different than yours, you can run into problems with the brand as a whole.
Boot height is another thing that will largely depend on your environment and what you're trying to do. Most of the time we see 8", 6", and 5" boots. Different height boots will provide varying levels of protection and support.
Lower boots offer a wider range of motion with your foot at the expense of not protecting your ankles or offering that additional support. Lower boots are also easier to lose. Moving through a swampy area or bog is already not fun, having your boots get sucked off your feet makes it even worse. Low boots in heavily vegetated areas or deserts generally warrant gaiters of varying length to help supplement the lack of protection and to keep things like debris, sand, or critters from getting inside your boots.
Taller boots offer more rigid support for mountaineering or difficult terrain and help protect your ankles, but are generally hotter, heavier, and give you less of a range of motion which can be important for running or moving between pieces of cover to advance toward an enemy.
The mid cut boot is a hybrid of the two, and offers you some additional support and gives you a decent range of motion while providing some protection that can always be supplemented with gaiters as well.
If you're wearing "waterproof" boots, they're only going to keep out water that is lower than the top of the boot. Makes sense since you need a giant hole on the top to put your foot into. If you're crossing knee deep water, it doesn't matter how great the Gore-Tex on your boot is, it's going to be wet inside.
Speaking of Gore-Tex, the waterproofing on your boot is something that to me is largely the most difficult decision. Waterproof boots generally have a Gore-Tex lining, or something similar to Gore-Tex made by whoever makes the boots, IE Danner Dry. Like said previously, your boots are only as waterproof as they are high. This means that if you have a 6" tall boot and you're standing in 7" of water, there's a good chance that you will get water in through the top. The Gore-Tex also makes your boots a little warmer since you have another layer that ultimately traps in heat. The idea behind Gore-Tex is that you have pores small enough to not let water in, but let water vapor out to keep the heat out and let your feet breathe. In my experience it isn't perfect, and in general you either get something breathable or something with Gore-Tex.
If you're going to be in standing water for a long time, in snow, or in an area with a lot of low puddles it's better to have Gore-Tex in my experience. An area that's mostly dry with some water crossings and decent heat, it's better to have a non Gore-Tex or adjacent boot. This will allow you to cross the water, change your socks, and keep moving.
Materials And Build
You generally have leather vs synthetic boots. The main difference between these is that leather naturally has some water resistant and breathable qualities, it can be reworked and serviced to have a very long lasting life, and it's very durable. Synthetics on the other hand are generally able to breathe better in warm or hot environments, will drain water quicker if they're filled, have less of a break in period, and are generally cheaper.
You also have a difference between stitched sole and glued sole. Stitched sole boots can be resoled so that you have a nice broken in boot with a new sole. Boots with a glued on sole tend to be more replaceable, and when they get worn down you throw them out for another pair.
Two boots that are well known in each category are Danner Acadias and Lowa Zephyrs.
Danner Acadia. This boot is a leather and Gore-Tex boot that is fully recraftable and resolable. This allows your boot to last much longer overall versus a "disposable" boot. The Acadia is also 4 pounds per pair.
This is a Lowa Zephyr Hi GTX TF. The boot is largely made of split leather and fabric, with a glued on sole. These boots are 2.4 pounds per pair, so about half the weight of the Acadias with the same height.
Something to note is that every pound on your feet is like an additional 5 on your back in terms of long term endurance.
Insulated boots are something I have little experience with other than the Mickey Mouse boots I've used on different occasions in the military. For general purpose stuff I generally don't use insulated boots but supplement the lack of insulated boots with heavier wool socks. This doesn't always work as well as insulated boots, and in extreme cold (-10F and colder) it's definitely better to have insulated boots, especially if you're sitting for a long time hunting or in an OP watching over an area.
The insulation in boots is generally measured in grams, the actual weight of the insulating material they contain per square meter. 200g insulated boots are not 200g heavier, but they have 200g per square meter worth of insulation in them. A 400g boot is not necessarily twice as warm as a 200g boot, and the temperature range of different insulating weights is difficult to pin down as everyone is different and everybody has different levels of blood circulation in their feet as well as other factors.
200g of insulation
200g is generally good for cool weather at lower activity levels, or cold weather at moderate activity levels. These are generally fine if the temperature rises a bit, so they're good for mild climates. Roughly 30-50°F
400g of insulation
400g is good for cool weather at low activity levels, or for cold weather with moderate activity levels. 200g and 400g boots are generally useful for the same range, but will depend more on the end user's feet. These are better for 30-40°F
600g of insulation
600g will keep you warm in cold weather at low activity levels, or around 15-30°F
400g-600g are generally good as work boots in colder weather.
800g of insulation
800g will work better when you start getting into very cold environments with activity. 0-30°F are fitting for these boots.
1000g+ of insulation
1000g+ of insulation is when you're in extremely cold environments and need more insulation at the cost of weight and mobility. Depending on what weight of insulated boot, you'll be good between 15°F down to arctic and subarctic conditions.
Selecting A Boot
This is the real question. How do you determine the boots that you want, and that will serve you well. Unfortunately like many things, it's not a simple "X boot is best for everything," and will largely be mission dependent and situational. As many would guess, it's generally better to be able to have boots for different situations than to have one set of boots for everything. Unfortunately, good boots are expensive.
If you're in rocky mountainous terrain you'll need different boots than somebody in the everglades. If you're somewhere that routinely gets cold and snow, you'll need different boots than somebody who's in the desert.
The best things to look at for factors are the weather/climate, terrain, moisture, and how long do you want these to last. Obviously everybody would prefer to be able to buy one pair of boots for their entire life, but Danner Acadias in the desert or in the swamps isn't going to be a good option due to the qualities of that boot. Work boots generally aren't ideal either since they aren't made for traversing terrain and the soles are generally made for concrete floors vs dirt, mud, and rocks.
Since I live in an area with 4 distinct seasons and climates with occasional heavy fluctuations in temperature and snow in the winter, I've opted for my "general purpose" boot to be Gore-Tex. I've had to do a number of water crossings in my Lowa Zephyr Mid TFs, but I generally will change socks and insoles afterward. Carrying extra insoles and socks is the best way to mitigate water retention issues with boots, as the insoles generally absorb a lot of water and wet socks + wet insoles can cause blistering as well. I personally didn't see the need to get insulated boots and will generally supplement by wearing thick socks, but there have been times where my feet were definitely cold even with thick wool socks, and if a sock is too thick in your boot it can restrict your blood flow and cause your feet to stay cold. This is why I generally advise against wearing multiple sets of socks unless they're both thinner.
All of this being said, I can use the same boots all year around with some minor issues in the winter and summer, nothing being life or health threatening. I chose the mid height because I don't live in a rocky or mountainous area, and choose to use gaiters to supplement when I need my ankles to be protected from debris and critters.
I had previously used Adidas AX3 mids, and after about a year the waterproof lining had stopped working completely but they were always comfortable in a mix of city/concrete walking and off the trail. Trail runners in general are usually very comfortable and have a lot of good features that you should look for in technical footwear, but are generally not meant to last long. Additional pairs for the boots you like should always be stocked if you plan on using the same boots for the rest of your time.