I don't really rate Crono. He's the player avatar, so the amount of personality he has depends on how much you project on to him.

Marle
Frog
Magus
Robo
Lucca
Ayla

Keep in mind though, that this rating is on a very small scale. There's only the tiniest of gaps between each character, or even between Marle and Ayla. It's rare for me to get a game where I like the entire cast this equally, but then Chrono Trigger hits rare milestones everywhere.