My best team? The Big Three (or the Original Three, if you would): Crono, Marle, Lucca. Marle Hastes everyone and heals, and joins with Lucca for Antipode 3. Crono just whoops butt on his own.

But after a while, Haste becomes pointless against anyone but 2nd and 3rd form Lavos. So my next choice is:

Crono, Ayla, and Frog. Crono beats everyone up, Ayla beats people up too and steals their lunch money, and Frog can beat everyone up and heal you.