Head shape matters. I struggled with a specialized helmet for a year, and I fell in love with several from their line, but the Giro/Bell helmets just sit on my head like a glove. I find the Specialized to be more narrow from front to back, while the Giro is more round, which suits me. I wish the Specialized fit me better, but they just don't. Try both brands on first. I have found them consistent between models, so even if you cant find the exact helmet, you can usually judge size from anything in the line.