Trunks was cool when he killed Frieza and then he spent the rest of the series getting beat up by someone.
And for the record it's unfair to mention how "cool" any DBZ character is if you haven't watched it in it's original Japanese version.
I was a Trunks fan as a kid, but now that I'm older and watched DBZ in it's original dubbing Vegeta is definately my favorite character.
And Gohan sucks.