Well, it depends what you like. If you like a nice Fantasy story, with mellowing music, good customizable abilities, fun minigames, good levelling system and don't mind about the old graphics, then FFVII is for you.
If you prefer a Charlie's Angels style game with annoying music, great graphics, a lot of hidden missions which easily spoil the story since, I assure you, you will miss them (unless you follow since the beginning a 100% guide which will spoil the game, your choice), tedious subquests that will take ages to be complited, sometime looking at most unimportant stuff regarding the story itself, but vital for the 100% completion, then choose FFX-2.