Tough one.
It occurs to me Laguna and Co. never dropped low enough for me to see their breaks. I'll have to check it out.
As for the others, I was always most exited to get Squall's, with Quistis a very close second just because of the options at my disposal.
Come to think of it, I've only seen Seifer's when I'm on the recieving end. Hmm...
As for Zell, I've never actually pulled off "Armageddon Fist", though it seems easy enough. Do I just keep hitting the button combos as fast as I can, regardless of whether the menu is on the screen or what combos are on it? I've been waiting for the menus to show up and trying to pick from the options there, which usually results in a random assortment of attacks, sometimes followed up by a finisher.