This is something I know a thing or two about
I was a huge ATV'er. 11 years thats all the wife and I did for our weekends/ holidays. Group rides, road trips, lodges, mud runs, poker runs, charity rides, cross provice, cross country, Technical competition... US and Canada...we did it. Between the two of us there have been well over 20 quads pass through the stable, from ALL the major manufacturers (except Polaris...way too many came out on a tow strap for me to be comfortable owning one)
I've owned:
Yama

350 BB, 400 Kodiak, 450 Kodiak, 660 grizz
Kawi: Little bayou, KVF 360, KVF650 and a Brute Force 750 Twin
Suzuki: Eiger, King Quad 300
Bombardier: Traxter 500, Outlander 400, quest 650
Honda: Rancher 350, Rubicon 500, had a rincon 650 for a week.
Artic cat: 400, 500,
Tell me what you want to do with it and I'll tell you what the best bike is.
Best work only machine? Toss-up between the 'zuki KQ and the Bombardier Traxter (both discontinued)
Play Machine? Loved the Grizz. Not a s quick as the Kawi's, but suoper handling
Raw go-fast power? Bombardier Outlander 800...stupid fast
best handling? Rincon 650
Hunting usage? Kawi 360
Mud machine? Brute Force 750
Whast it comes down to is that there is not one true "Do all" machine.
Want one? You need:
Honda Engine (hey..it's a Honda!), Yamaha's automatic (NEVER buned a belt...it's always under tension), Kawis 4X4 (progressive hydraulic diff-lock...no electronics Bomb's "visco-lock" is a real close second)), Kawis rear brake (Clutch pack inside the rear drive shaf...NO maintenance!), Honda's susoension (from the Rincon only) and the seating of the Outllander Max.
At the end of the day, after owning the "latest and greatest, biggest and baddest" quads, I now have only one: The KVF 360. It was one of my wifes first bikes, and it does everything I ask of it. Minimal stuff to go wrong (no electronics/liquid cooling/Fuel injection) to worry about. I can submerge the thing up to the handlebars, and have it back up and running inside 30 minutes using trailside tools.
Check out our ATV website and ask there...I'm sure you'll get a response or two. It's ATVwild.com. Check into my forum (Hunting and fishing) and say hi :0