Best try first simpler (from game mechanics perspective) game types like action games, platformers, etc. You can still make great games in those categories. You can easily see some great examples of this in this jam games.
RPG games are far more complex (even if you tone down the mechanics). Plus they require lot of time for balancing, testing, etc..
And time in a game jam is the one thing that you don't have ;-). Even in a one month game jam like game off.
You can always try later after you gained some jam experience.
In any case good luck with any future jam games. And keep making games!