I've been riding bikes on and off for over 30 years (dirt & road bikes and quads) and I ALWAYS wear a fullface. If you're going to buy one don't sell yourself short, DON'T BUY PLASTIC, polycarbonate or whatever they call it.... Spend a extra few $$$ and buy either a fiberglass or Kevlar helmet.... If you do a face plant you'll be glad you spent the extra bucks!!!
You can get some good deals on Ebay, HOWEVER go to a bike shop first and try a few on. You'll find that different manufacturer's helmets fit differently. Bell helmets tend to fit narrower heads best while Arai will fit a rounder shaped head, etc. Also the newer Bell's are a wee bit heavier than the rest as well, so a lot of it depends on personal preference. Don't expect to spend less than $350 - $400 at a retail shop for a quality lid.