I strongly advice against best roleplayer, comment and favorite hentai artist.
Simply because they can be easily manipulated, hard to track down and could pretty much just become a clusterfuck. Not to mention that some poor girl will be named and then basically kill her inbox.
The other ones seem reasonable, the favorite user specifically because that comes down to just "Who was the nicest guy". Its not really diminishing like something like "Roleplayer" could easily become.
The best way to do that would be to set up a forum post (By a mod, do not do it yourself) in which people can name the person in the category. Like this:
-Best Tagger: Person
-Longest Serving User (Still Active): User
-Best uploader: User
etc.
That could be locked after a certain amount of time and then counted out. That way we can spot accounts that basically registered to vote, can have a mod delete unnecessary things, and yet remain open about what is voted for.