The TRX-4 Sport is exactly the same, except it doesn't have the 2-speed and diff-locks, so it should be even more reliable with fewer parts, and you can also upgrade the transmission and diffs down the line with conversion kits. And I agree with @Pat_ranch that the Sport Kit is a good option...
For versatility, I think the TRX-4 is a very good choice (though it is kind of on the expensive side). Here's a pro/con list I came up with for the TRX-4:
Pros:
- Bulletproof drivetrain
- High and low gears of the 2-speed have a lot of contrast (goes from very torquey to super fast instead of...