I thought about the Giro Xen myself but it was pretty expensive and I was right in the middle of sizes. In the ned I got a MET Crackerjack - which I think may even be a youths type helmet (or just for smaller heads) anyway had more vents and a more comfortable fit than the equivalent Giro. Looks pretty good too. I tried on a wide range of helmets from the very expensive to the very cheap.

I'd say try on all the ones you like if you can, what looks the best and what fits the best can really be two different things and turn out completely different to what you thought was ideal through online research.