Depends. On my favorite playthrough (the one that I took seriously and wasn't trying to get cheevos or anything like that) I'm a ruthless colonist. Batarian slavers killed my colony so I killed a bunch of batarians on an asteroid for revenge. I tried to make him come off as a cold, cold bastard with some deep seeded anger issues to everyone but his close friends like Anderson, Joker, and eventual LI. Its interesting, because almost all of the renegade options in the first game fit really well with this mentality/backstory. Its particularly fun "warming up" to your new crewmates, ie you being a complete asshole in the beginning (renegade options) and then slowly befriending them as you progress through the game (paragon options). As you progress through the games you can either make this version of Shepard lighten up, by slowing picking more paragon options, get consumed by hate and pressure and be a complete bastard, or pick a little of both. I always liked to pick a little of both (with slightly more renegade) because it just made the character seem more human. Plus it was just fun watching everyone be wary of the badass "Butcher of Torfan" when in reality he's just an normal dude. Also I never got how a sole survivor Shepard would be okay working with Cerberus in ME2. Particularly since one of the most traumatic experiences suffered was caused by them.