Tipperary and Troxel are both good brands. Where I work, anyway, Troxels are a little cheaper, but Tipperary are more comfortable/adjustable and look nicer.
And, yeah, I'll agree with Cannoka. Those Western Hat helmets are the cheesiest thing ever... I'd only ever consider one if you want to look silly! XD
If you can, find a store nearby that sells the helmets. It's always better to try them on, rather than guess!