I think it really depends. The most obvious answer is KD. But when you're in an objective game, I couldn't care less about your KD if you're the one carrying the ball or delivering the flag. Also, I think there's a lot to be said of people who are supportive--the ones who increase morale, do callouts, and are always there to pick up the assist. I've seen too many people who have great KDs but are crappy communicators, and thus bad team players.
In short, I think there are a lot of areas in which to be skillful, and you don't have to master them all to be considered a skilled player in my book.