Depends on what you've deemed as 'fun' though.
Assuming a traditional game, with standard rules and roles (ranging from BM to Paranormal)
The benefit to being 'town' is in detective work. Folks that have fun here are the type that catching people in their mistakes. Finding out that Mr. Perfect Town isn't as aggressive as he seems to be. Throwing that one question at Ms. Clean that sends her into fits and stammers. Pressuring someone until they CRACK. Turning the tables on a bandwagon that's about to lynch you into the discovery of an entire scum pack. Finding clues, mistakes, contradictions, that seperate town from scum. That's the gain of being a town.
Those that enjoy being scum most enjoy the manipulations. Seeing an entire pack of people, dedicated to locating you slide by your name as if you don't exist. Sitting back while the messages and confusions you've set swallow a town whole. Altering facts. Abusing people's failures. Seeing every plan fall together. Watching the town 'hero' fall into your trap. Leading the town to tearing apart their only hope for survival. That is the gain of being mafia.
Now if you are looking for something else, you are probably looking for something non-standard. Some people like being able to control and use game altering powers. Those are the role heavy games, like KWN and BYOR. Some like puzzles, trying to break down a system and 'hack' it to their advantage. Bastard games are designed with that in mind. Still others like to just completely mess around. Odder games, like what KotM has turned into, form that, along with some BYORs with the right host.
Of course, the first question is: what sort of 'fun' are you after.