My favorite was the revolver with explosive rounds. It's a one-hit-kills gun against unarmored enemies. Pretty funny actually. I also used the silenced, laser sighted pistol with armor piercing rounds for stealth (headshots). Both weapons are strong
and take little inventory space.
I use the tranq. gun a fair bit. It's virtually undetectable and for a while I was really focusing on getting the pacifist achievement. Since giving up on that achievement for the first time around (realized I may have already messed it up in the
beginning), I decided to start using my fully upgraded Combat Rifle. It gets the job done. lol