Goku vs Vegeta. Though we got a taste of it with Raditz, Goku had to pull all the stops of his new training just to damage Vegeta, and even then it wasn't enough. He needed help from everyone there, including Gohan in Ape form just to beat the Sayian Prince. It was a really epic fight. Goku vs Frieza comes close, but that one fight was so epic to me. The classical beam fight between G Gun and Kamehameha is a cherished memory of mine!