I've got this.
(You should've posted this under Off-Topic / Manga/Anime)
Full Power Super Saiyan Goku's Kame Hame Ha was probably stronger than Vegeta's Final Flash.
[Full Power SS Goku] Kame Hame Ha > ["Super Vegeta"] Final Flash
["Super Goku" / "USS"] < ["Super Vegeta"] Final Flash
Trivia: Had Vegeta's aim been more true he probably could've killed Cell. The problem with the situation was, Vegeta was 100+ feet above surface, and he had to make sure he didn't destroy earth in the process--had the situation been in his favor, and had he directly hit Cell, it would've been over.
Goku's Kame, which was probably stronger, was also shot at pointblank range.
The Final Flash, in comparison with most, is a much more powerful attack, because it was designed to draw in & unleash as much energy as possible, where an attack like the Kame wasn't--but the amount of energy the Kame can generate depends on 1] how powerful the person charging it is, and 2] how much energy that fighter wishes to put into it.
Spirit Bomb > Death Ball