A client sided hit detection code with full lag compensation up to around 200 or 300 ms is most likely the best way to go about it in a game where most guns are hitscan (as in the bullets are instant and not projectiles). Enemy Territory has this and it is extremely consistent.
I'm sure most FPS gamers are aware of the amount of frustration you experience when your aim is directly on the target when you fire, but the bullets simply don't connect. In some games this happens extremely often (look at Black Ops or Bad Company 2 for example), but some games actually have a good system in place and it is extremely rare that your bullets don't connect. This can really make or break a game for many players and I hope Brink does not fail in this regard.