Chiaotzu. I don't remember him really beating anyone, all he did was blow himself up to no avail.
Videl on the other hand (spoiler warning) helped Goku become a Super Saiyan God, which in turn saved the Earth. She's also literally a crime-fighting superhero in her spare time.
If this was a battle thread, then obviously Chiaotzu would win, but Videl has been more "useful" as far as I can tell.