Fit is all that matters.
I have a Giro 9, which I love. I bought it because it is the only helmet that fits my melon, but love it because it is the lightest helmet on the market, and it has incredible venting. I am always hot when I ski, and a full, heavy helmet with average venting is not an option.
Try on as many as you can. Ski shows can be a good place to do this, as you can see all fo the different models and talk to the reps. Buy something that fits and that is comfortable. If it isn't, you won't wear it, and that misses the point. Good luck.