It depends honestly, if you don't mind olfschool RPGs I'd say the 4th and the 6th are pretty good to get into the series The 7th didn't age well on many aspect but it's a classic FF10 is The other games are all controversed (with fans and haters) so it's hard to say which one would fit you the best

But the ones I named here are generally considered to be some of the best games in the series