Of the ones I've used:
Cateye Micro is OK - does the basic stuff (average speed, distance, time, max speed), comes on automatically once you start moving and has a light, but the mount is rubbish. Mine rattles around so much that I've had to pad it out with blu-tack.
Topeak Panoram V12 Widescreen in wireless is excellent, IMO. The fittings are really easy to use, and re-usable, rather than being just a couple of tie wraps. The display is enormous, and it automatically returns to the first screen, where it constantly displays trip distance, clock and current speed. I've had it for about a year and a half, I
may have had to replace one of the batteries. and only once has it packed in working. On that occasion, it was raining so much, I had to take a five mile detour to work to avoid the floods
I've also used one of
these, and it's brilliant to have the information on altitude & gradients, but it's a bit over-complicated and it did once completely give up the ghost while I was in the middle of nowhere, which isn't confidence-inspiring.
Oh, and I like wireless computers because they look neat and are much easier to fit.