The first party I beat the game with was Crono, Marle, and Frog. Worked out well, enough since I won.
For the longest time my party to beat the boss was Crono, Robo, and Marle - a single max cyclone would take out the left bit, and Robo/Marle's dual tech Cure Touch cured for full hp. Robo's shock dealt decent damage, and Crono's luminaire is one of the best spells in the game, so I wasted ass pretty fast.
My current beat the game party is Crono, Robo, and Lucca. Crono and Robo still take out the left bit on the first turn, and Lucca's Flare does a lot more damage than Ice 2. The reason I changed is becauise I found out that Robo's second cure spell (Cure Beam?) also cures for full health most of the time, and the loss of Haste isn't a big deal because you can't speed up lvl. 100 characters with maxed speed much anyway.
Yes, I still have the first save I made on my SNES cardridge when I first got Chrono Trigger and have been New Game +'ing it for... wow, is it close to 7 years the game has been out?