I have played and enjoyed every single Final Fantasy game. Even XIII has some great stuff going for it. The series strong suit is that it’s never stale. Each game is a fresh, new take on a somewhat familiar net of design philosophies.
My favourite is XII. I love its job and gambit system, as well as the world design and music. IX comes just a tiny bit short, then V, probably.
Please let Mars crash into the Earth. Really enjoyed Majora’s Mask, looking for more immersion.