I second the above advice. My priorities:
- Safety (but they should all be certified)
- Comfort, not only size and good fit system, but venting.
- Another issue is I want the vents to be skewed enough so that I don't tan or burn my scalp from any sun angle, especially overhead when the sun is most intense. (My current helmet FAILS on this point.) If not, I need to wear a thin cap or put a white paper towel inside the helmet, which obscures venting. This is hot weather only, in cold it's gray out or the sun is low or I have a fleece hat on under the helmet.
- Large enough to fit a fleece hat underneath (with my size head, barely on current).
- Effective sun brim in front.
- Reasonably attractive appearance.
- Moderate price.
- Reasonably aero.