I wouldnt say I have a favorite,but FF7 had by far the most to do.
The side games were incredible.Doing a battle tournament for materia,Raising chocobos and racing them...I spent alot of time building up my characters and maxing them out.
FFX was great too,the ultimate weapons quests could be annoying (hi lulu) but once you finished them,it was rewarding.
Also liked 4 (obviously from the avatar) because Cecil and Kain were badasses.
Every FF game was great(exluding the mmorpg
) but those 3 stick out.