I think Omega in FF5 was bang on. The ability to inflict pain in many different ways, a tricky status to bypass, and a weakness you had to be clever to bypass.

Rebuttal

(BTW, aeris2000x2, all three of the above mentioned bosses were incredibly easy to me....I guess I was just luckier than most. Save (SPOILER)Trema, I hardly considered any of 'em Super bosses, and even the above mentioned was disappointiongly easy. But getting to him was interesting.