I would have to say yamaha. I have a yamaha quad that I have been riding for a few years now with no problems. My friends and I spend around 30 hours a week (durring the warm months) riding hard on the sand dunes here in St. Anthony and the ones of us on yamahas are upgrading, adding parts, and making them faster, while the others seem to be spending a lot of time and money fixing. Granted we ride them hard, but it just seems the yamahas have held up the best.