The first 9 are excellent games. I haven't played X, XI, or XIV, but I have played XII and XIII, and personally I don't prefer them (XII was awful, XIII was average at best.) I don't recommend the spin-offs, except for Tactics, which is actually very good for a strategy game.
I should note that if you're getting into Final Fantasy from Kingdom Hearts, good luck, because the two have very different gameplay styles, at least from what I've played/seen of Kingdom Hearts. Final Fantasy is turn-based (though from IV onwards, battles are in real-time, but still played in turns), as opposed to the real-time real-space battle mechanics of Kingdom Hearts.