I admit to being a bit of a Luddite... I'm about 10 years behind everyone else, and if anything technologically goes bad... I start searching for a 12 year old.
On my tt bike, I was perfectly happy with any computer that showed speed, average and time. Except that I typically use a Hed Trispoke up front, and while carpet tape USUALLY holds a computer magnet... on 3 race occasions, it didn't.
Funny thing, that. What is really grand is that on the days that I didn't have a computer, I rode about the same speed as I would ride with one, and once rode faster. Much faster. (I think it has something to do with all the predict your mile time stuff I did when I was a runner...)
To solve the computer thing, I bought a Garmin 305 for the tt bike. Problem, you have to charge it for pretty much every ride. Since the Garmin has to be charged, I have left it at home, on the charger, when it should have been on the bike at a race. That's strike one. Strike two is that the little computer really likes to have its data downloaded into your PC. Except that I'm a Luddite, and I just don't do that.
Garmin has replaced my 305. Multiple times. Those guys at Garmin are just wonderful. I'm still not going to down load the data, and the 305 will continue to lock up after a few hundred rides. And I'm sure the nice guys at Garmin will continue to replace it.
I finally got tired of charging a computer for the road bike, and just got a cheap Cat Eye Strada. Know what I hate... those little arrows that tell you that you are going faster than your average, or slower than the average. I have to turn that sucker over when I go out for an easy ride, as my competitive nature makes me want to keep that arrow pointing up.
What do I need in a computer... average speed, time, distance and current speed. I do miss an old Specialized computer that I had years ago... it told you the current temp. Like you really needed a computer to tell you that it was stinking hot, when you could look down and see the tar bubbling on the road. I may not be a sophisticated geek, but I am a geek. I loved knowing that it was really 115 degrees on the road... you know, where we ride. Too bad I knocked that sucker off the handlebar one day and we could never find it.