If you like MMOs then FF11 is one of the more hardcore ones.
WoW is for people who don't like or know much about MMOs, but want to play one, so it's a fantastic newbie MMO.
FF11 is for grinding hours on end, on end, on end, on end. And then you're like level 20 and you've completed maybe .1% of all the leveling.
You just have to put a TON of time into FF11. WoW you can play casually and still accomplish things. And you can do battle arenas which i hear are a blast and very unique.