Honda or yamie, just like uncle matt suggests. I have owned both and it boils down to personal likes as they are both solid ATV manufacturers.

FWIW I have a 05 450 Kodiak at the moment, that has over 1000 miles many hard. The only thing I have done is change oil. Great little bike from my perspective. Previously I have owned Yam Big Bear, Honda 300 TRX and Honda 400 Foreman..all were extremely reliable and good investments. I have also owned polaris...don't go their is my advise. Far to much wrench time required for my liking.

Used is a good option if you can wait for the right bike, I have bought the majority of mine this way. You'll find as Matt says many guys buy them then unload them b/c of lack of use.Biggest fear you have is lack of maint. of the bike. Look over the general appearence but makesure to check the levels, air filter, etcand never buy without taking a test rip.