It's difficult to go for anyone but Schala for me.
Marle is alright, but she has a certain tomboyness and wildness I don't like. Sort of like "HEYYYYY YEAH LET'S DO THIS WOOHOO". I like enthusiasm, but it can be overdone.
Lucca is alright too. Actually I kind of like her character I think, she's not selfish at all, and she doesn't brag a lot even though she's way more intelligent then most of the crew. Only thing is, she's so nerdy and the big glasses and all.
Ayla... Too prehistoric... Over the course of Trigger she gets better, but still... I couldn't see myself together with her.
As for Chrono Cross, there's a whole lot of more options here, but still not many appealing for me.
Kid is cool, but wayyy too tomboyish, like, way worse then Marle. She needs to open up a little and let go of that tough girl act.
Leena is sort of cool, but she can be kind of hot headed and selfish. Bitchy. Same with Lisa from the element shop.
All the other girls in Cross is no no. Harle is cool as a character, but that french accent and the outfit would drive me crazy in time.
But Schala... Schala is so... Selfless, caring. Warm. It's like, she always worries about others before she worries for herself, always. None of the other girls in CT or CC do that. Everyone has at least one moment where they're being selfish, but Schala never has that. It's a bit unrealistic, but really appealing.