Final Fantasy VIII had exactly six party members, and three of them (Squall, Rinoa, and Selphie) were always on my shit list. Hell, I wouldn't have taken Squall to the final dungeon if the game didn't make me. A big part of the problem is the RNG for their limit breaks, meaning that you're incentivized to (in Squall and Rinoa's case at least) deliberately not upgrade them in order to maximize the chances of them rolling the good shit once you get it. Selphie, even with aura+menu refresh cheese, just can't be relied on to produce a worthwhile effect in less time than it takes any serious opposition to murder you. Irvine gets a dishonorable mention because of his resource-consuming limit, but it's reliable damage which is more than I can say for, say, Fated Circle.
Zell and Quistis are the best, IMO, because they produce reliable effects when you need them- and Quistis is absolutely vital for power leveling in Heaven and Hell via Degenerator. Blue Magic is underwhelming in a lot of Final Fantasy games here, but when you can learn it from items here and pick up spells like Degenerator, Mighty Guard, and White Wind early on in the game, she's basically got a unique spell selection that you don't need to actually stockpile.