1. Honda: The best for engineering, frame geometry, brakes, suspension, reliability, light weight.
2. Yamaha: Stronger engines than Honda per cc. Close to Honda in the other categories.
3. Suzuki/Kawi, flip a coin: excellent quality, closely following the design and manufacturing levels listed above.
These manufacturers began their ATV designs based on motorcycle frames, engines and suspensions.
The other major players started w snowmobile technology: Heavy, undersuspended, less reliable (struts, belts and clutches instead of shocks, chains and sprockets, for example).
My biases about ATVs comes from my training and experience as riding instructor. I'm done w mechanically complex bigfoot quads, even though I'm old and slow. My current atv was chosen for simplicity, handling, light weight, enough power for fun and CO high altitude, reliability, ease of maintenance/repair. And good news, those = low cost of purchase/ownership.