If you don't mind a real manual footshift, Suzuki and Honda both still offer true manual 500 cc bikes (Kingquad and Foreman) if you wanted the ultimate manitenance free machine.
Lots of people buy Polaris and Cat's and have reasonably good luck with them if you dont ride much and maintain them well, but I don't think many will recommend them as a whole.
Sticking with a Kodiak 450, Foreman 500, or Kingquad 500 would be the safest longterm bet. Kawasaki makes a nice bike but do they make a 500 class or just the 650?