Heard good things about GPX. Made by the same company as the Unison and Kolpin from what I understand.

 

Look at the Hyosung 100 quad, over here in NZ they are covered by Kawasaki warranty.. But are approx $600 US cheaper than the Suzuki. Out of the box they are faster, l have moded our one up now, buy removing restricters, and the head gastkit so goes like stink now. It runs rings around moded LT 80s as well...

 

Both of the KYMCO's 50 and 90 ATV's are superb.
They are supplying 250cc atv's to artic cat.
They built Honda motorcycles for over 20 years since the 1960's. They are still a Honda supplier.
They are a little less than the top 5 brands, but you don't lose any quality... in fact you will probably get a superior product for less!
and a great warranty to boot.

 

Jetmoto 150cc is also an amazing quad for the money, absolutely no complaints here.