VIII has imo the best story, and the best main charachter development (Squall and Rinoa go really deep, and Squall changes a lot... but the rest of the charachters are pretty flat and can feel almost irrelevant). Triple triad is fun too.
VIII however has imo the worst gameplay of the first 10 games (still fun, but imo the worst), so I can't consider it the best
I personally like IX best... the story is good, every character (except Amarant) gets a good story, the gameplay is the best one imo, it has a bunch of minigames and sidequests, the soundtrack is the best imo,... pretty much gets everything right
idk how you could call someone who says VI or VII are the best a moron, as those games are great too. VI has by far the best cast of characters in the whole franchise (so many of them and yet all of them gets their own story!), and VII modernized the franchise (and the whole JRPG genre) in a good way and created a great story about taking care of the planet, and it also has the most iconic antagonist of the franchise
The first 10 FF games are all so great you could pretty much make a case for all of them being the best... X with all those sidequests that bring hours and hours of fun, IV with those dramatic moments, V with a very fun 4 main characters, III with those gimmicky dungeons and its hard difficulty,... perhaps only the first 2 feel like the worst because of how their ideas have been recycled and polished in the following games and the fact they pretty much have no story