I can probably think of more than 10 times that were great, probably but not 100% sure on that fact, but at least 10 Kamehameha's that have defined the series. This includes all Dragonball series (OG, Z, Super, GT) and the Dragonball movies as well (because despite most movies being not cannon: the Super movies excluded, some of them have amazing Kamehameha moments.)
I'll be counting downwards, so 10 to 1, with 10 being good but not amazing and 1 being what I feel is the best. I'll kind of give my reasons why I like these or maybe why they were significant.
It may have angered Vegeta but he saved all of them in the end.
It also created one of the most iconic poster moments in Dragonball history, Goku on the ground shooting the Kamehameha up as Vegeta shoots the Galick Gun down and they clash in the middle. A clash of titanic moves and the beginning of an intense rivalry that would span the entire series. While some may be cooler looking than this, I felt that not only does this look cool that it plays such a large part in the Goku vs Vegeta rivalry going forward that it can't be overlooked as the top Kamehameha.
IT IS ONE OF THE MOST ICONIC MOVES IN ANIME.
DESPITE MY LOVE OF OTHER CHARACTERS MORE, YOU NO DOUBT HAVE TO RESPECT GOKU AND HIS KAMEHAMEHA AND ALL THE AMAZING MOMENTS IT HAS HAD IN OVER 30 ALMOST 40 YEARS OF EXISTENCE.