It depends on the mission....currently in my playthrough of ME1, I rely on Garrus and then switch out the 2nd team member ...Ashley and Wrex have worked well.
In my playthroughs of 2 and #3, I tended to take the "Tanks" with me....Garrus, Wrex, or Grunt....except during the suicide mission at the end of 2
Mordin Solus. Yes, i know It's not Garrus, but hes at a close second. I love mordin because of his attitude towards everything, and i thought he was just a funny character, also i fell in love with him when he sought to do justice in Mass Effect 3, when he cured the Genophage. I also loved him because he had that awesome combination of Cryo and Incernate tech powers. I always had him for that!
ME1: Garrus,and Liara.Being a mentor to Garrus,and a friend to Liara. ME2: Garrus,and Miranda. Garrus my sidekick,and Miranda my second-in-command also romance option. ME3: Garrus,and James. Garrus once again sidekick,and James the new guy who needs a mentor. That's about it.