Originally posted by PhoenixAsh
Character wise Squall versus Seifer, given Seph barely acknowledged Cloud until very late in the game and they weren't competing for anything so it's hardly rivalry.

Gamewise VII versus VIII. I've never seen any other obvious rivals.
I agree with all of that except for the game rivalries. I'd have to say that the FFVI and FFVII rivalry is the biggest/greatest rivalry.