I prefer wired computers, as they have proved more reliable and problem-free in my use than wireless.
Given that, it is no surprise I prefer wired computers with a robust wire that is unlikely to tear, crimp, or split. The head unit also has to be waterproof and the spoke magnet should also be robust and made of metal, not plastic.
One that ticks all the boxes for me is the Planet Bike Protege 9.0. It has a large screen easily visible even in low light, is proven waterproof, and has no external buttons (the head unit shields the contacts from water and slides on the mount to select different modes).
It does have one very annoying flaw if you ride lots: The average speed is calculated on a 10-hour timebase, so any rides longer than 10 hours show an Error reading instead of average speed. This is a huge disappointment on a 17-27 hour day ride. Otherwise, it works well and reliably and can be found here in the US for as little as USD$24.
Best
,
Dan.