unions are usually pretty burly bindings, but i have a big problem with their ankle strap! the actual strap is about an inch or so wide and it causes some pressure points. this strap also has a tenancy to stretch after a few weeks of riding. so the binding that fit your boot so wonderfully, is now too big. major bummer. they are also a bit heavy. but like i said earlier, burly. it's also pretty easy to find replacement straps and bolts from your local shop!
Rides on the other hand, are very light! their straps i find much more comfortable, especially when combined with ride boots! (if they fit your feet well!) however, their highbacks tend to be really really stiff with not much give for those tweaks. some of the ratchets they had for a few years there are VERY sticky. make sure to try strapping into your boot before you buy them. and if i can give you ANY advice, DON'T EVEN THINK about getting the contraband bindings. they break and then you are S.O.L.!! it happened to quite a few people i know who rode them every day.
but i think at the end of the day it really comes down to how the binding fits your boot, how stiff you like your highbacks, and what you're riding. i liked my unions better than my rides in the long run. much more forgiving and last longer.