[LUW]

There are so many models I would say just get something that you like the looks of and are willing to spend.

That's pretty much it. The functions are very similar between them, so you basically have to choose the one you think is cooler.
BUT, there are a few key differences. Some models are Tough Solar (solar powered) while others are battery powered and some versions have radio-sync capabilities - the "atomic" models. The Riseman is an ABT watch (altimeter/barometer/thermometer), while the others aren't, and the Mudman has more stopwatch features then the other two.