Having owned only 4 quads (one from Polaris, Honda, Yamaha and Kawi), I can say that my 99 SP335 was the worst by far. I won't own another Polaris.
3TV should chime in here as he's owned probably 20 different ones in the past few years.

 

1997 suzuki quadsport 160. Had a year to play with and it fell apart. The front axel even broke!!! It was a pile!!

 

I had a Honda Odesy. One of the earlier models with no rear shocks. It was fun to ride but it had an air cooled engine that sat right behind the seat where no air got to it. I was always seizing pistons and scoring the cylinder.

 

I owned a 89 lt500 quadzilla for exactly one desert trip. I picked it over a banshee because I was 14 and the 500 sounded big. In one desert trip I:

Snapped the clutch cable
Throttle stuck really bad on it.
Lights would be bright and then dim
the cap blew off the silencer(really that was fmf's fault)
And the bike heat siezed three times.


I got home, sold it and have ridden my 86 tri-z 250 untill yesterday when I bought a YFZ 450

 

my 97 scrambler 400 . 3 engines all on the 6 month warranty.

 

thats normal cuz quadzillas don't have batterys.

 

Yeah, but they would dim when I was on the throttle. Ususally they only dim when you are off the gas. The stator was probobally bad on it.

 

Most of our quads have been great but if i have to find the worst I'd say my dads 87 bayou 300. When it runs it's a pretty good quad but thats kinda rare. It hasnt run for about 10 months now and I'd rather ride my quadsport so I doubt it's getting fixed any time soon, unless my dad feels like working on it.

 

I had an old Bayou 300 in the 80's and I tell you it was the most reliable atv I have ever owned. If I put the miles on my Raptor that I put on that 300 Bayou I would be on my 15th transmission. The worst atv I have owned would easily be my Raptor.....but it's a blast when it's running.

 

I wouldnt own a polaris more than 2 years old!!!!!!!!!!!!! they seem like they know they have problems in them and want you to buy parts for them. Although they have gotten better for reliability as of late. My friend had a 96' 400 scrambler and its the biggest piece of Junk i have seen. Also i know a guy who had a 1993 trailboss. He shut it off on the trail and went to start it again. The starter didnt work. so he had to pull start it. the pull start rope broke. ( he said he a took a log and beat that thing for at least 10 minutes) he had to walk 5 miles to his truck through swamp.