Damn, guess I gotta be the odd one out here, neither Goku vs. Vegeta fights rank that highly for me, neither rank into my top five. Not that I hate them, but I'm not sure either would make my top five, the Majin fight might.
My favorite fight in Dragon Ball Z is actually Piccolo vs. Android 17. It's like the only major fight that doesn't feature a Saiyan (the only other one I can think of is Videl vs. Spopovich), and it's one of the only fights that's evenly contested all throughout. Like, most fights in Dragon Ball Z rely on the dramatics of momentum shifting, so there's a lot that features prolong segments of control from one combatant which hey, works wonders dramatically but I find the fights where they're basically equal all throughout to be more entertaining to watch. The moment that puts it over the top for me was the Hellzone Grenade, seeing 17 dodge all those shots only to discover he got himself surrounded was cool, one of the very few instances in DBZ where it felt like actual strategy and clever utilization of ki was actually important. Always find stuff like that more satisfying than just out-powering your opponent. I know it kinda ends in a draw because of Cell, but that doesn't hurt it much for me. I also really like the post-fight stuff, like the kinda bonding moment of teaming up against Cell between the two.
Outside of that, Cell vs. Gohan is another favorite, and the best climatic battle the series ever featured, and Goku vs. Cell was another excellent, evenly contested combat with another actual strategy/clever utilization moment with the Instant Kamehameha which is the slickest Goku's ever been. Outside of the fights from Dragon Ball Z's best arc, I love Super Buu vs. Candy Vegito fight entirely because of how ridiculous it is that Candy Vegito was absolutely squashing Buu. I'm still upset that Candy Vegito has never been playable in a Dragon Ball game yet.
