Secret Areas (AS2R) - Intro
Self-Treatment: Slowly regenerate health
Quick Learner: "Knowledge/Intelligence" points. Advance quicker.
Economist: Discover more money. In more places?
Night Vision. Most useless perk.
Vampire: Drain health from enemies to add to yours.
Hypnotist: Control enemies to attack their own kind.
Observer: spot hidden areas with a briefly appearing red error on map. Most useful perk.
Boxer: Punch enemies if not equipped with a gun. Most useless perk.
Character to choose
Pick anyone you like, but I suggest strength over anything else. In Alien Shooter 2: Reloaded, strength determines how much ammo to carry. In Alien Shooter: Vengeance, strength determines how much equipment and ammo you can carry and is CRITICAL.
If you want a fragile girl against the invading alien horde, I recommend Nina Rossow for your character. You can choose color of your "armor", and add to her skill (green plus signs).