Good wireless = good
bad wireless = very bad
A lot of it is a looks thing. Wireless looks cleaner, and is easier to set up on a suspension fork. Also, wireless can be more rain resistant.

I've got an old Cateye Enduro wired on one bike, and it has never given me any trouble, rain or shine.
Another bike has a Supergo wireless that will pick up false input from traffic light sensor loops, but otherwise has given me little trouble.