" Kid Buu.
1. Kid Buu is much smaller and faster than Hirudegarn who is much to large and slow to be able to touch Kid Buu who can teleport as well.
2. Hirudegarn's blasts have been shown to cause very limited damage while Kid Buu's energy blasts are at a level which they can effortlessly destroy planets.
3. Kid Buu can regenerate from virtually any physical damage he has sustained and cannot be harmed physically leaving Hirudegarn's attacks nearly useless.
4. Kid Buu is more destructive and dangerous than Hirudegarn and if character morals apply he could simply incinerate Hirudegarn with a large energy ball or energy blast.
5. There is no possible method which Hirudegarn can use to functionally harm Kid Buu.
6. Kid Buu has matter manipulating abilities and there is no evidence contradicting the fact that he could simply transform Hirudegarn into chocolate or candy or whatever he imagines.
7. Kid Buu is functionally immortal and cannot die through conventional means.
8. Kid Buu possesses unlimited god-like stamina and agility.
Kid Buu wins. "
I was going to go into some detail as to why Buu would win, but Newdeath did it for me. I agree with everything here, well put.