I bought my helmet, I got a Troxel Intrepid. It fits well, I guess I have more of an oval head because it doesn't fit my 11 yr old daughter as well as it fits me, her head is more round like her daddy.
I got the black one since it was the only color they had.
I have an Ovation Deluxe Schooler. It's dial fit, which I'm not a huge fan of since the teeth get worn out after a bit, but I do love that it has a removable liner you can wash. The chin strap comes with a nice felt pad which is also washable. The excess strap is bundled up with two rubber bands -- I roll those up and over the felt pad to keep it in place since the Velcro doesn't really do the job. The venting is a lot better than the old Troxel I had.
I have the Troxel Sierra - I like the look of it and the ventilation is good. I wish it fit a bit better but I think the adjustable band does a good job.
I hit really hard at the beginning of summer - had a concussion and brain-bleed and won a 4-day stay in the hospital for observation. This was in a sand arena, and you can see where the helmet absorbed the shock. No splits, but there's a flat spot and a dent on opposite sides of the helmet (landing and then the shock moving the material). I landed on my back hard enough to bounce and flip over onto my front, and lost about 15 minutes of memory. Happily I healed pretty well and uneventfully and bought another Troxel Sierra - I figured hitting that hard and having relatively minor injuries was a good recommendation.
However - it all depends on the shape of your head and having the helmet properly adjusted to fit. So get a helmet that fits your own head and then wear.it.every.time.