Well to be honest, i find VIII the greatest of them all. It felt more matured, more realistic and had the best music. On terms of story i think VIII had more depht then the others. Especcialy the rivalry between Squall and Seifer was even more interesting then between Cloud and Sephiroth.
When i played the game, it almost felt like i was a soldier (Squall) and needed to grow stronger and rank up (SeeD level). Those buttons combination during Limits Break was enjoyable and even hard to do. Also i think they worked out those summoned creatures (GF) the best in VIII.
The card game in VIII was really entertaining unlike IX, you could win cards and trade them for items. Searching the whole world for the right cards and it didn't even got me bored to be fair.
To be short VIII is the greatest FF of them all, but it isn't my favourite FF game to play.