i have a smith holt. its the only helmet ive owned. i tried on a lot of helmets though all of which weren't to comfortable though. i ordered online without trying it on (dumb i know). i took the chances but im very pleased with the outcome. best fitting helmet for my head thus far. looks sick and got it cheap on SaC.
but yea, i suggest you dont do what i do, go to a shop and try then all on.
I also wear a Smith Holt (with Skullcandy from the factory) and I have a big head. the RED cut into my forehead, the K2 felt funny on the top and the Giro XL was more like a medium
The big thing is find one that fits and is comfortable. A helmet that isn't will likely end up being used for loose change, and that doesn't protect you much. I've used mine twice now, and both times it would have been much worse. Kudos for thinking with (and of) your brain!