I use Bontrager, Cateye, and Sigma computers on different bikes. I like the Cateye Padrone, for its large display. I use it like a speedometer, tracking current speed and either elapsed time (if I'm riding a known course, and trying to better a previous effort), or average speed, which I use to gauge effort.

I do like the looks of the Wahoo RFLKT, which is more of a remote display for the tracking systems on your phone. Nice display, and very configurable.