Fit should be the deciding factor, I feel. That, and whether you want a visor or not. I replaced a serviceable cheap Schwinn-branded helmet with a Giro Atmos (I) a year and a half ago, because it fit me best. I ended up missing the luxury of the visor on the cheaper helmet though, and began thinking I'd spring for sports wraparound prescription glasses.
Lack of visor didn't stop me from wearing the new one, thank goodness, because I suffered a freak accident and ended up hitting the pavement squarely down (not flying, a rotational smackdown!) onto my forehead. I cracked the front of my helmet and had a mild concussion and cloudy head for a couple of days. But because the fit was right, and the Giro I had has a very easy adjustment, it did not slip and saved my eggs (well some of 'em). YMMV.