My 2 cents
7 is the ultimate FF but the PC version is gimped with Midi music files and the music from FF7 is incredible, though there are ways to import the ps1 music to the pc version and tart up the graphics if you can be bothered. 6 is great if like me you like the blend of sword and sorcery with technology, 8 has the coolest visuals but convoluted magic system for some but a great story if you into time travel etc. 9 and 4 are ok but very medieval not really my thing but still enjoyed them. 10 is a really cool story but this is where FF started really hand holding for me and I lost interest with 12, never played 13 and 15, 15 hardly seems like final fantasy at all its basically modern day Japan with magic and monsters. 11 and 14 being online guff so they don't count.
Take others advice here FF7 is an unbelivable game, the story, the characters, the music, the secrets, the optional bosses. Good memories of that game.