Humm..well mine would have to be Vegeta Super Saiyan 4's attack called Final Shine.[not final flash] And my other personal favorite is Bebi Vegtia's Revenge Death Ball. Last but not least Super 17's attack Electro Eclipse Bomb. whats your Fav Technique?!
You cant go wrong with the kamehameha it's always affective. It's always there for you when you need it, and can kill almost anyone. It's one of the first moves that was introduced to us, so that's why it's so good.
A underated technique that I like is Solar Flair where it blinds the opponents for awhile, I think that technique is to underated. I know it doesent hurt anyone, but lets say your injured and you need to take a senzu bean it will give you the time to take it.