FFXI is a massive timesink, especially compared to WoW.
Be prepared to completely invest yourself in FFXI if you want the experience, WoW is much more "fun" from being so casual.
I played FFXI for over a year, I could go on and on about it, but frankly, it only appeals to certain people. If you don't want to spend your weekends standing around town seeking party, if you'd rather be playing the game one way or another, just play WoW.
Edit: Wow I can't type.