I would spend as little as possible on a simple wrist computer, and buy a brass/glass SPG like the XS scuba. Oceanic, Aeris, and Suunto all make simple wrist computers; the suunto gekko is one, oceanic veo100nx, aeris XR1nx. These all do nitrox and provide all the dive info you need.
IMO people buy expensive computers because they like gadgets, which of course is perfectly fine, but don't expect a more expensive computer to improve your dive experience. Some people like to download their dive profiles and are willing to pay for that; others want air integration, saving them the "terrible inconvenience" of having to look at a SPG, and are willing to pay (usually quite a bit) for that.
The important things are: 1)easy to read and understand display, 2)clear N2 loading bar, which is very helpful near the end of a dive when you typically use your computer the most, 3)the ascent rate indicator and alarm, and 4)the conservatism of the algorithm that the computer uses to calculate N2 loading and off-gassing. It's important to understand that conservative computers have absolutely no better track record in preventing DCS than do liberal ones, even though that seems counter intuitive. There simply is insufficient data, and too many variable outside of computer selection, to make any conclusive statements about computer safety comparisons.
