VII is the best. Story, characters, art style, music, gameplay. It's all 10/10 for me. The GOAT!
IX is amazing too but I feel like it has a couple small issues holding it back. The combat is waaaay too slow, the Trance system is a huge downgrade from Limit Breaks, the optional card game is not optional, and I'm not the biggest fan of the art style (bring me Nomura or bring me death!).
I won't fault anyone who picks IX, but VII is THE Final Fantasy game for good reason.