One that hasn't been mentioned is the Bombardier or whatever they are calling them now...Can Am I think.
I think they are all good but after having a Yamaha and riding a host of others, I bought a Polaris Sportsman 500. I like the one lever, all four wheel braking, all of the storage compartments, and, where the Polaris really shines, the on demand AWD. In 4x4, it is only in 2wd until the back tires slip a little then it is in all wheel drive. This is very minute, and unnoticable. It does this in milli seconds several time while driving so that you can still steer and have a tight turning radius. While there are others that you can stop and lock in all fours, the Polaris does this for you on the fly and is in and out of bad spots before you could even shift the others. The drawback to this system is the engine braking. Because the rear wheels have to spin slightly faster than the front before 4x4 kicks in, only the rear wheels will hold you going down a hill. Once I got used to this, it wasn't a problem as the one lever, all wheel braking does the same as engine braking only manually.
Polaris is a US company too.