i have a 09 700FI Grizzly and i love it.It has on and off 4x4 and front diff lock which i really like i have used it to cut and haul firewood, drag tree tops out of a tangled mess in a logged woods, plow snow, and just all around trail riding. it is fast and reliable and anything with fuel injection is a major inprovement over older carburated models. my buddies have 850 polaris's, 750 brute forces, and 750 king quads and my machine is just as or more capable than theirs. The grizzly is a single cylinder motor while the other ones are vtwins. the grizzly seems to have more low end power with the single cylinder than theirs.its all in what your personal preference is the only thing i like better about mine versus mine buddy's new 2010 850 polaris is that mine weighs 350 pounds less, will still pull as much, and run right with him in on the straight aways. In the woods mine is much more agile and shorter wheelbase which makes it easier to manuver and faster on tight trails
I have an 04.5 700 efi and have never replaced or repaired anything on it. I use it for plowing and pushing brush and gravel and pulling. The only thing I've done is replace the oils and a battery last year. BY FAR the smoothest ride and I hear the 2010's are even better. I would get the optional power steering though. I ride my 2 and 4 year olds around and it can get a little difficult to steer sharply with one hand. Also remember that you don't need diff lock on a polaris because it is already AWD not that 3 wd crap that the others do then ADD diff lock.
My brother owns a 2004 Yamaha 660 Griz, and I own a 2004 1/2 Polaris Sportsman 500 HO, of these two, the ride on the Polaris can't be beat. "If" I were deciding on the two you mentioned, it would be the Polaris without a doubt.
The Polaris comes with 2 gear ranges, high range and low range, most problems occur when some people aren't in the right gear range for doing what their doing. I never had a single issue in the 5 years owning mine.
yamaha. Have had nothing but trouble with polaris reliability wise.
But like someone else already mentioned, it maybe spotty. Some guys say they never had a problem. But that may also be due to lack of understanding there is a problem. Not that I am calling anyone out. Im jus sayin
Go with the Yamaha. My 2008 Polaris overheats, sometimes just doesn't start, the winch relay failed, and now has a blown front CV joint. Only has 116 hours on it. Pure junk, I find myself relying on our 1987 Honda 350 4X4. I'm dumping the 800 in the Spring.