S.T.A.L.K.E.R.: Clear Sky

Stalkers are definitely better than bandits, and easier, because the bandits are overrun from three directions by Duty, Stalkers and Freedom.

Clear Sky can't not be chosen - they won't let you out of their base.

Duty and Freedom are quite similar - Duty are stronger, tend have a better strategic position, and be better at fighting, but Freedom are friendlier, and give you an exosuit if you win. IF you don't hate the whole lot of them for the insane trader (not much of an improvement in duty) and the traps around their base.