It's funny... I wouldn't actually take my favorites I don't think. The first two are easy.

FFXI because there's a ton to do and I actually really do like it.

FFXII because even though I don't care for the story, there is a lot of gameplay and tons of side content.

After that would have to be VI or IX. VI is probably my favorite, but IX would keep reminding me of all of the other games and keep the nostalgia fresh in my mind.