I've never played FF IV or VI, so I can't say anything about Tellah or Umaro, however I can offer somewhat informed opinions on the rest of them:

I generally didn't like Cait Sith due to his general uselessness, not to mention that his limit breaks were way to random for my liking (Yes, my final party against Sephiroth consisted of Cid, Cloud and Yuffie with fully charged limit meters, marking me forever as a munchkin, but I like to have as much firepower on my side when dealing with enemies of that caliber), but I didn't really hate him per se....

Rinoa was my favorite character in VIII for a variety of reasons, not the least of which was that she was a girl who could think up some kick-arse plans (I like smart girls), and was really good in a fight as well.

Quina had a slightly annoying personality, but I like blue mages (nothing like taking one of the bad guys tricks and using it against them in my book), and s/he was undoubtably handy in a fight, and was well balanced, not to mention that in places where I couldn't get ethers on a regular basis (like 90% of map), Quina's 1000 needles attack (with a 5 MP cost) was the best deal going, especially against ranged enemies, and enemies resistant to normal or magical damage (1000 needles ignored defense and always did 1000 points of damage).

Wakka, I liked, because of his cool Jamaican accent, mon. Plus he dealt some major long-range damage and could almost always kill flying monsters in one hit.

Rikku was my favorite charachter in X due to the fact that, again, I like smart, spunky girls who aren't afraid to speak their mind. Not only that, but thanks to Rikku, my party never had to buy potions. On top of that, during several boss fights, Rikku's Mix overdrive got my butt out of a jam (wether it was mixing a hi-potion and an antidote to get a super-elixer that healed the entire party and removed all status ailments or the time I used a similar formula to make a ultra-phoenix and used it on Elvrae Altana and took off almost half its hit points in 1 round).