I'd say, use the one which (in some context) reflects something of you in some way or is somehow (to others, not necessarily gamers) kinda very much 'you' in some strange, funny way.
For example - all my GamerTag and PSN User Names I use with GTA are all, in some fashion, identifiable as either sarcastic references to some of my old RPG characters and Car Wars driver names. They are totally meaningless to others on the whole, but those who knew me from those days, kinda identify me from them (and gameplay style).
You can just invent something that just is whatever it is, make it significant to you, portray some kind of implied message - it's down to you to figure out the whys and how
One of my GTA combos is a nickname of 'TheFiddler-UK' and the signature vehicle used being one of many customised vans with a license tag/plate of '
COTF' - to any fan of the old road movies, especially from the cult stuff, would identify those as being keyed into a particular psycho driver - i.e. The Fiddler (so nicknamed for his tendancy to drive aggressively to some psychodelic bluegrass fiddle heavy music whilst terrorizing his victims in a souped-up panel van) and DCOTF being short for '
eath Car On The Freeway' (the movie title).
So just go with whatever isn't taken and you can get away with that suits your way of thinking