There are so many good choices (Bell, Simpson, Pyrotech, Bieffe, etc etc) at a pretty low price point ($250-600)...ultimately, fit is the whole deal. Find the helmet that is the most comfortable, while still being snug at all points of your head. Try a number of helmets on, wear them around the shop/store for a little while, make sure no strange pressure points (a small pressure point in the shop can cause major pain in a 30 minute session) and buy what fits, IMHO
I'm currently using a Simpson Shark (Sidewinder). Kevlar full face with helmet cooling attachment. I also use a HANs device. The combo is not cheap, but... my wife would be really upset with me if I paralyzed myself and wasn't using a good helmet and HANs device.
Last year I used a Simpson Bandit which is more cost effective (also can have HANs device attached.)
Great setup Subdriver. Do you have a cooling box also?
I bought a HANS in 01 after the front roll hoop stopped my head from moving forward as the (racing) steering wheel bend inside-out. Switched to a not as good system when the HANS prevented exit in the fixed door car.