I like Crono, Lucca and Frog.
It just seems to be the best balanced party.
Here you have mega attacks like Luminaire and Flare, and also a character who shines
in both the fighting and healing department.
You get all elements for the battle against Magus, too: Lightning, Fire and Water. t3h sweetness!

Crono, Robo and Ayla is cool too, people from all eras meeting each other.
I thought it was pretty funny.