How do you figure? The number of characters who change in any significant fashion from the start of the game to the end of the game can be counted on one hand.

Seifer is well-characterized in that we know what drives him and why it drives him. We clearly see his fall to temptation as well as his steady degeneration as it becomes clearer and clearer that he's just being used. Seifer starts off the proud knight and he ends up a feeble fool clinging to an illusion while everyone close to him abandons him.

The only emotional connection you can have to any character in the game is pity for Seifer.

But fine, I will rephrase. In terms of characterization, Seifer is the best FFVIII has to offer.