I think that I'd rather live for a moment then live forever and do nothing. As for changing the world I don't know what that would be but it would have to be something pretty big. The idea of living forever is kinda intriguing but at some point i think I'd go insane. (not that I'm not already)
As for a character I'm going to choose my own character Miles (name might change). I've been taking a while to develop the character Miles and I've kinda based him off myself. For example, He's cocky, insane, lazy, but smart when he wants to be. There's a lot of differences though because i think he would want to live forever. Living forever would be meaningless because all you friends and relationships would change as time goes on.