What is the best party in ff13?

The best party in FFX is whichever you feel is the best.

I, for one, used Tidus, Wakka, and Auron throughout the game, save for the places it demanded high-power meatwalls (Summoning with Yuna), Magic nuking with Lulu, or I needed to steal items.

The best party is whoever you like the best, basically.

I personally use;

Yuna - All round healing, good with black magic later in the game.

Tidus - Fast and agile, strong. Also make him learn White Magic for extra support against bosses, monster arena and dark Aeons.

Auron - Really strong, high defence and high HP but is slow, good for tanking against bosses and being a major damage dealer.