I can touch on a few things here.

We ( the wife and kids) often spend a few weekends in the summer riding ATV's. Went to the Hatfield/McCoy trail system last year. I ride often and have ridden ATV's for many years.

I also have friends and family that also ride. I am not a brand loyal type but there is one brand I wouldn't want even if I won one on a ticket I'd sell it. That is a Polaris. I had several friends that had themand they had nothing but problems. I know others will dissagree, but the aren't very reliable in my opinion.

My personal ride is a 660 Yamaha Grizzly. I love it.

My wife has a Honda Recon.This is a good ultra reliable little quad.

The boy has a Yamaha Warrior. Also reliable but no mud protection. Its a sport quad.

The daughter has a Suzuki Ozark. A Fun little quad and very reliable.

We are not brand loyal as you can see. I have also owned Kawasaki and had no problems. In my opinion, all the Jap brands are good reliable machines with the Honda being just a tad above the rest in this department.
Can-AM ( Bombardier) are also good machines. The 800 being the top dog of all big bores. More power and speed than the others. Their only problem is the are way too expensive.

Test ride as many as you can and read some of the reviews in ATV magazines.