The issue with this question is that FFXIV has not been active long enough (assuming we forget about the mess that was 1.0) for it to really be considered.

Quite honestly, I played FFXI for eleven years, and STILL have an active subscription because I STILL log in at least once a month to catch up on some content. Granted, I solo gods on WHM these days, but I spent years putting together an appropriate frontlines combat cleric so that I could rock Vana'Diel in D&D fashion.

I feel like XIV could easily become my favored game of the two (I obviously put more time into it these days, but it's fresh and new) but at this point in time, I still have to answer with XI.