I havent had anything but negative experiances with arctic cat quads. their sleds on the other hand are perfect.
Honda, in my opinion, are by far the best built machines out there. for whatever the purpose. they put up with anything you throw at them. as a proud and former honda owner of quads and bikes they have put up with everything and have been completely reliable.... until you swamp them
Polaris, I dont mind... but they could use some improvements. I dont have a need for anything higher than a 500 sportsman. my buddy owns both 400 and 500 HO's at his camp. the trails are ROUGH! rocky as heck, muddy like you wouldnt believe. just hell for those machines and they put up with it time after time.
Can-am (bombardier), I used to love their stuff. still do actually. havent ridden any or have friends that own anything bigger than a 350 rally. from what I read and heard, they're pretty solid machines.
Suzuki, my buddy's father owns a big 700 king. pretty good bike by the sounds of things. but the yamaha bruin can get through mud holes it cant.
Yamaha, once again havent had much experiance with them. nor have I heard too many good things. but they may be quality machines for all I know. well, my buddy owns a bruin and its a pretty good little quad.
I may have forgotten a manufacturer. hope this helps!
Edit: Most quads you're gunna find now-a-days will be belt drive. though they aren't half bad I still prefer shaft. at least that way you dont have to worry about belt slipping and snapping etc.
JP