Second String: Hey, when do we get to play?!!!

VII: Yuffie, Cid, Cait Sith 'cause they don't really contribute to the story or life in general.

VIII: I used everybody equally.

IX: Eiko, she's just weak and pointless.

X: Because of the machanics I used everyone.

XII: Penelo and Ashe.

VI: Gogo, Mog, Umaro, Strago, Relm, Setzer, Gau, and Cyan. I only really used Sabin, Terra, Celes, and Locke, and sometimes Edgar and Shadow. The rest sucked, in my opinion.
X: Kimahri, just because...well, he's Kimahri. And he couldn't do much damage unless he was in Overdrive.

gogo can do everything(except increase his stats) Mog has the moogle charm, gau is possibly the best in the game if used right Strago is a blue mage which is always good and character wise cyan is one of the deepest most brilliant ever created.

I do agree about umaro and relm but part of the reason VI is so great is the different ways to play through it using different characters and the fact that besides terra being the "main" character, almost everyone is equally important in the grand scheme of things.

Of course, your just answering the question but VI is the hardest for me to even identify a second string... Hmm... yeah relm, umaro and setzer.

VI-- gogo's inability to increase his stats makes him noticeably crappy compared to everyone else. Big deal, he can bum rush. It seems awesome until you notice that Sabin is doing 7-8 thousand damage with it and gogo is doing 3-4 thousand. The other is Gau, who really is useful, but I know I'll have to leave someone at the ship at the end, and while everyone is useful, the other characters don't require me to spend a good 6 hours on the veldt.

VII--aeris is a waste of experience. And no one likes cait sith.

VIII-- Zell's limit breaks were harder to pull off

IX- Amarat and Dagger were the only two who weren't God-like.

VI - Usually Umaro and Gogo (except in the collesium) Because they dont get any damn lines!

VII - I like to keep everyone equal but if i had the choice i would chuck out Cloud just to see where things went.

VIII - Same as above with Squall

X - Lulu's limit break was pretty pathetic.