If you're getting a raptor, don't get a 660, if you let it sit for a few months ever the carbs go to **** quick and if you want a Banshee, leave it stock unless you want to work on it A LOT.
Best quads to buy just to fvck around with are Hondas, super reliable, always start, simple carb systems, takes me literally 30 minutes to clean the carb on my 400ex, and takes that long just to take the plastic off of my dad's raptor.
I'm not biased, it comes from experience, I've worked on Polaris, Honda, Yamaha, and Kawi's of all different shapes and sizes.
EDIT: Btw my 400ex does 50+ Stock, no exhaust mods or anything just a K&N filter.