I'm new to the ATV scene. I got a Polaris Sportsman 500 EFI about a month and a half ago. I have over 350 miles on it so far. It ranges from flat as glass speed runs on a dry lake (indicated 58, reality probably 52 with GPS), sand, dirt "roads", desert washes, etc. I have been in places that I probably shouldn't have gone but the capability of the quad was higher than my good sense. :-laf The only problem I had was rough running and backfiring. Turned out to be the Mad Dog tank bag. The neoprene that goes over the tank has a hole for the filler. The cap is vented through the bottom and the neoprene didn't let it vent.
The IRS is awesome. My buddy rode behind me on a solid axle Honda and noted that the Polaris looked a lot more stable in the bumps, ruts, and off cambers. The transmission is a centrifical clutch type, with H, L, R, N, P selector on the right side. No problems there. It is recommended to use L range for constant riding under 7 mph, pulling, or plowing. Mine also has EBS, or Engine Braking System. It is amazing. Going down steep grades in lose rock, you don't even have to touch the brake. You actually have to stay on the throttle a little to keep moving. It will stop, and hold, the bike in place.
The only thing that I don't like a whole lot is the racks are composite instead of regular tubing. Makes it kind of hard to attach stuff, especially on the front rack, though I was able to attach a pronghorn antelope and ride 4 miles with no problems.

The front rack does open to a small storage area. I keep a shovel and fire extinguisher in there, though you could fit some emergency gear in it.
Polaris has a 700 and 800 model if you need the extra oomph. Kinda wish I had it, but don't really see the need unless I was going to be pulling, hauling, plowing, etc. I definately recommend looking at the Polaris, just to check it out. Polaris also offers a 2-up seating arrangement (the X-2) that is slightly longer than the single seat. Good luck and have fun. These things are a blast!