Personally, I would never buy anything Polaris. It just seems like everything they make is junk. I don't know - I try to give them a chance every year, but all of their stuff is just so unimpressive. A buddy once had an older(early 90's) Scrambler, and that fricken' thing was in the shop more than it was in the dirt. Went like hell through damn near anything, but it was a real POS.
Bombardier makes a good quad. Out of these two, the Bombardier is better, hands down.
If you don't mind looking around, I would suggest trying to find an Arctic Cat. I've ran a total of 5 of them, from early 2000's to basically brand new, and I've never had any significant problems with any of them. Mechanically, they just can't be beat.
Honda's are pretty damn reliable as well. They're not my cup of tea, though -> The cat's have some advantages that make them more appealing to me.