As far as features in an atv, I decided after owning a few, that the following were absolutes:
- independent suspension. If you are gonna spend any amount of time on it, especially trail riding, your back and body will thank you. On the flip side, you lose some ground clearance when loaded or towing compared to a straight axle.
- fuel injection. No messing with a choke during a cold start and warm up. I found some machines to be very finicky in this regard, not so with EFI.
- front diff lock. Without it you are essentially driving a 3wd machine. Nothing more fustrating than getting hung up and finding that the one front wheel that is in the air is getting the drive sent to it while the one on the ground is sitting stationary.
- automatic. I did not like to always be shifting gears, especially when group riding where the speed was being determined by someone else.
- winch. If you are going to be riding alone, this can be a real blessing, even if you are trying to be cautious.
As far as brands, I have owned Honda, Yamaha, Suzuki, and Arctic Cat. I have found that there reasons why Arctic Cat (USA) and CF Moto (China) have a lower price point compared to the Japanese machines of similar displacement. When compared side by side, the differences in engineering are obvious. Axle and driveshaft diameter, A arm and suspension components, frame structure - Japanese machines are superior in almost every regard in my observation. A pet peeve of mine is the braking system on Arctic Cat (now Textron) and Polaris machines that only offer a singular control, as compared to others that have separate front and rear controls.
I own both an atv and side by side (utv), and find that both have their advantages. The atv is more agile and able to navigate tighter trails, while the utv is a great machine for touring and hunting purposes in less confined areas, with lots of room for gear, and protection from the elements.
As always, your mileage may vary.