I don't remember a lot fights in DBZ, but I think Majin Vegeta vs. Goku. Because this is emotional and excited to see them fighting again. I feel with vegeta, because I understand what he got through and how hard he trained to beat Kakarot. (Coughs Goku) I know they both are strong and I'm glad that Kakarot (Goku) didn't kill Vegeta at all in the begin.

But damn you Frieza for killing him! You overgrowth lizard that you are! I'm glad that Kakarot (Goku) Killed you! I know it took 3,5 hours that fight. It's pretty long and the longest in the anime history.