Yuna > Rinoa > CC Aeris > the rest
I find that those three are the only real love interests. Yuna and Rinoa are pretty obvious since they actually spent time with their other halves in their games. CC Aeris has the benefit of two games to build her relationship with Zack. Yes, you played as Zack with amnesia in the beginning of FF7.
All the rest are laughably bad or doesn't spent enough time with their partners to even be considered love interests.