What kind of screen name do i use?

Depends what it's for. If it's for a game then put something cool so if it's for a game like mech quest then put something like razorhawk21 or if it's for something like stardoll put something like cococherry72. If it's for a site like this one just put your normal name coz the first one would make you seem really tough and the second one might make you look... well I dont really know but don't use that coz I'm using that

If its for Job Hunting, or for Resume use you should have a nice scree name.