From playing FFXI for a year and WoW through Open Beta plus retail I can honestly say they are completely different MMORPG's. One's a more time investment, and one is a more casual playing.

If you can't spend a bit of time in a game, then I wouldn't bother with FFXI. But if you just want to 'pop on and get something done quickly', then WoW is for you. I don't think any other MMORPG will suit you apart from WoW, and don't even mention Matrix Online (*cough*).