Sonic.

Of course mario is used more, but that doesnt stop galaxy being one of the best games of all time and seriously giving me the sense of wonder i love from mario games!

FF on the otherhand has gone downhill since VI (except for IX, and yes VII is pretty good), so far nothing ive seen of FFXIII makes me think that it is anything other than a rehash of the VII principals with nicer graphics...

I think the question should be which one will wear out its welcome sooner.

It took 5 pages for somebody to bring the winnner. We can fight and nit pick about our own personal feelings about Mario and FF being overused but sonic and Crash Bandicot sit there showing us what really happens to overused IP's. Too much strain is put on the IP for whatever reason ( yearly releases, chars being forced into situations they don't belong in with out taking the time to make the games good, riding the name brand and putting out bad games in the ip's orignal genre , ect ect.) and it's name dies or becomes equated with shit games. Nintendo takes care of their plumber and his crew because while he shows up in every frigging genre, he rarely graces a bad game. The FF IP...... well i'm going to fall back on sales here and say when these games start to tank they have been overused, to aviod going way off topic.               

If overuse is justified by change, then Mario is overused.

I just don't want to see the day where I have to obtain licenses to wear hats in a Mario game.

They're both overused, but they're both good series of games.

Now Guitar Hero is wayyyyyyyyy overused, and it's the same game every year except when they added drums (to copy rock band) and new songs.

mario is the most overused.
It'll soon be to the point where if you have a so-so idea for a game you just add mario, and it becomes a fan favorite.

that's just how it seems

By some people's logic here if you took Super Mario and switched Mario and the others with a complete new cast and a new storyline it wouldn't be overused anymore?

I did this math before. There was something like 100 titles with the name 'Mario' in it and 68 with the title 'Final Fantasy' in it.

However, the spike in the number of titles tagging the 'Final Fantasy' label to themselves has jumped so much, its almost overtaking the rate of Mario titles in percentage. And in just the last generation, since the DS/XBOX360 came out (Nov 2004), there's been over 40+ games with the title 'Final Fantasy'.

^But they have different stories and thus aren't overused :p

would they sell as much? no.