Well, in forum mafia games I've played an interesting variety of roles.
DBZ Mafia I was an item-based, preventable, 3-night-delay, one-time use killer. Basically the weakest thing ever.
MaFEa I was part of a 2-player, 3-alias wolf faction. Two aliases could inspect and Namecheck on even nights, and the other could kill on odd nights. It was a pretty fun role to have, as far as they go - despite terrible playing on my part. x)
You Choose It Mafia, I was a silencer, which was also really fun to play as. Being an actually useful role, and being able to stick around most of the game, I managed to get successful silences almost every night. Definitely my favorite role in a big mafia game so far, even if yci wasn't my favorite game.
Viva La Mafia was fun - though that had nothing to do with my role. I was a one-time blanket safeguard (which dak ended up forgetting about, which allowed Brain to get my role pm... >_<) and a
one-time announce.
Small mafia games have provided me less interesting roles.
I've been Mayor, Silencer, Thief, Vanilla Villager, and Hooker. Out of these roles my favorite was easily hooker. Thief and Silencer generally end up at the whim of someone more powerful on the team, but hooker is usually top dog. Thief in Touhou mafia would've been great, had I actually stolen something.
On IRC mafia, I've always been fond of the Inspector and Silencer...
