Here's a side-by-side of the three...
Obviously the one I have the most experience with is the Dozier (mainly because I've had it quite a bit longer).
Blade-wise, they all use AUS-8 steel, and all appear to be heat treated well. The RAT-2 and Zancudo are FFG, whereas the Dozier is hollow ground. The Dozier blade stock is slightly thicker as well and maintains that thickness (as measured along the spine) for almost the entire length of the blade. The RAT-2 feels like the best slicer between the three (purely subjective based on me slicing through some corrugated cardboard at the moment).
Ergos-wise, the Dozier does have a longer length of usable handle. It is also the only one of the three I can get a good 4-finger grip on. I can get 4 fingers on the Zancudo as well, but it is a bit of a tight fit. The RAT-2 does have a bit of a thumb ramp, as well as a nice flat space from the top of the handle to the blade tang, which makes choking up on the blade possible. The Dozier has some usable jimping as well, although not as pronounced or grippy as the RAT-2.
For handling (opening & closing), the RAT-2 is by far the smoothest of the three. The thumb studs on the RAT-2 are also the most comfortable (digs into the thumb less while still providing good traction). The liner lock on the RAT-2 is also the easiest to operate one-handed. The Zancudo's frame lock is pretty stiff and does dig into the thumb a bit to operate. The back lock on the Dozier can be operated one-handed with a little practice. Both the RAT-2 and Zancudo lock up very solid. The Dozier locks up securely as well, but due to the liner-less handles and back lock design, does have a little bit of movement in all directions (FRN handles flex, and just the nature of back locks).
For carrying, the RAT-2 does offer a 4-position clip, and it is also the most discrete (least amount of handle exposed) of the three. The Zancudo is set up for right-handed carry only (tip up or down), whereas the Dozier is drilled for tip-up carry in either left or right handed positions. All the clips hold the knife securely in pocket, although I have had the Dozier snag on stuff a bit more than the others.
Couple of miscellaneous observations... The RAT-2 does have hard angles on the spine, making it the only of these three suitable for striking a firesteel. The Zancudo has a beautiful stonewash on both the blade and framelock scale.
If I were picking some for gifts (not knowing all the preferences of the recipient), I'd pick the RAT-2. It's a good functional/utilitarian design, easy to operate (without having to go through much wearing-in of the knife or practice with the lock), good ergos, and offers a couple more carry options.