Usually ride without a helmet, for states w/laws I have a Jockey helmet, and for the winter I have a bell full face. 15 degrees is a little cold with the Jockey & a Neoprene face cover.

 

 

full face mostly, and 3/4 in hot humid summer weather. I crashed an older bike on a busy highway in the Bronx a few years ago and the right side of my face was getting scraped by the asphalt for about at least fifty feet. Luckily it was cold and I was wearing my full face helmet. This question brought up the thought that I might have ended up looking like Two-face from Batman, and the only ones who would look at me funny would be my two dogs lol. But I don't live too far from New England states that don't have mandatory helmet laws, so if it's an empty open road on a nice day, I'll strap my helmet to the bungee on the pillion.

 

Poll doesn't take into account that folks may have more than one helmet. I have FF and 3/4.