Like I said, I've only used a 510. But if your looking to broaden your search, consider the screwdriver. That was the first big battery pv I looked into. Ive had good feedback on it. Its 3.7, but I dont think the batts last as long. it says 8 hrs, but Ive heard a day.
Puresmoker, the makers of the protege, jus came out with a new 5v mod called the Prodigy V2. No one has it yet (to my knowledge), but considering the makers, and how excited people are over on the Puresmoker threads, Its definitely worth your interests. Its 5v.
There should be a poll about favorite voltage levels.