The Kid Buu saga had a lot wrong with it, with the series feeling a little long in the tooth at this point and the villain of Buu just not being nearly as compelling as Frieza or Cell were. His turn into Kid Buu helped change that a little, getting him out of the arrogant and overconfident mold that almost every villain in Dragon Ball Z seemed to be.
Instead, he was a chaotic evil type character who was like an untamed animal. He only wanted to destroy everything in his path, having little motivation beyond that. It didn't give him much depth, but he didn't need it by the end of the arc. The one drawback is many of the fights felt like filler (some truly being so), outside of his showdown with Goku.
9 Krillin vs Yamcha
This is a prime example of the filler mentioned, two training for no real reason other than to show what they were doing, a major flaw with Dragon Ball Z as a whole. Far too often episodes were insanely padded by checking in on characters who had no significance whatsoever to the moment at hand. The battle with Frieza and Goku being the prime example of that, with the fight going on three times as long as it truly needed to. Krillin or Yamcha didn't matter much anymore, a fact that gets proven when Kid Buu invades Other World.
8 Krillin & Yamcha vs Kid Buu
Low and behold, Yamcha and Krillin are no match for Kid Buu in a fight that was utterly pointless. It showed Krillin getting rag-dolled mercilessly and Yamcha acting scared of Kid Buu's power. The only net positive is it showed that Krillin is one of the braver characters in the series since he continually tries to fight above his weight class despite knowing what's destined to happen to him. He also actually hit his Destro Disk here, for what little good it did.
7 Pikkon & Olibu vs Kid Buu
As with Krillin and Yamcha, this wasn't much of anything. Pikkon teases Kid Buu about wanting training, laughing about it until Kid Buu starts getting serious. From then on he manhandles everyone in Other World, which is a shame since Pikkon is a cool character, one many would like to see be made canon.
If anyone deserved a little bit of shine in a filler episode, it was him. They could have at least made it a little bit competitive before Kid Buu eventually won.
6 Goku vs Super Buu
This was all filler before him reverting into his Kid Buu state. As such, the fight just felt like it was kind of there, padding for time as was often the case with the anime. If you wanted proper Goku vs Super Buu action, there was plenty in the last arc, which is where this fight should have stayed. Regardless, it was here and frankly no greater than the battles in Other World. The arc doesn't truly start to pick up until the confrontation between Kid Buu and Goku & Vegeta.
5 Hercule vs Kid Buu
This fight showed the importance of Hercule, letting him have an actual impact on the story while providing his usual comic relief. He shows up to make fun of Buu, acting all big and bad as he often does, only to turn right into the sniveling coward we all know once Kid Buu tries to attack him. Eventually, his pleas bring about the return of fat Buu or good Buu, setting up a fun little battle between the two of them. Most surprising though is that Hercule actually managed to dodge two of Kid Buu's attacks.
4 Supreme Kais vs Kid Buu
These fights may have been short, but they helped establish Kid Buu as the true powerhouse form and why it was the most dangerous one he had. He effortlessly destroyed two of them before coming up against South Supreme Kai, who put up more than a little bit of a fight.
He was the first that fell victim to the absorption technique, turning Buu into a mountain of muscles. Grand Supreme Kai being the last and second to get absorbed, leading to Fat Buu.
3 Good Buu vs Kid Buu
This fight is genuinely pretty good, even if Buu's durability was utterly stupid. There were some very inventive spots, such as Kid Buu ripping off his arm and using it as a weapon against Fat Buu or Fat Buu breaking apart to make body doubles of himself. The fight was pretty competitive too, as Fat Buu had more than a few moments before he was finally beaten by the superior opponent.
2 Vegeta vs Kid Buu
The fight tested and showed the level of resolve that Vegeta has. He was outclassed and knew it from the very jump, admitting that Kid Buu was far stronger than he was, yet, he continued to fight. Even as he was battered for much of it, he kept getting up, trying to buy as much time as he could for Goku. While he may have been the punching bag, Buu isn't defeated without Vegeta taking the beating that he did here. It showed that his pride was no longer a weakness he let control him.
1 Goku vs Kid Buu
While it may not be as good as some of the other fights in the series, Kid Buu vs Goku delivers in spades and may be one of the more underrated battles you'll find. There's very little stalling or downtime in it since Kid Buu isn't much of a talker, so it's just raw action from start to finish. It also shows Goku in all three of his forms, showing Super Saiyan 3 to its full capabilities. Kid Buu gets too look like an utter monster in it too, psychotically laughing throughout it. It also ends with the Spirit Bomb finally working after all of these years, the cherry on top of what is a great fight.