Resistance Fall of Man? Is that what you mean?
I would choose Half-Life. Sure the Combine exists, but they aren't invincible and the only defense they have are the advisors. I generally believe the vortugants will turn on everyone again as soon as the conflict is over. I hope not, but the events of the Xen crossover make me think so.
What is your weapon of choice in Half-Life? (Non-Gravity Gun).