Out of interest, what squad line-up did you favour in your first ME1 playthrough? I suspect a lot of people's preferences are dictated, or at least influenced my their gameplay choices the first time around. Personally I played as a soldier so once I recruited them, Tali and Liara felt like the optimal companions. After a while I just got so used to having them around, they became favourites. Prior to that I favoured Ash and *anyone* other than Kaiden. The guy irritated me.
For my first playthrough (Soldier Shep), my main sidekicks until later on in the game were Ash and Wrex. It didn't make for an optimal team, but I guess it worked out.
Before I finished the game I took a sidetrip out to Luna and decided to take Liara along. On that mission, she was throwing the drones around so after that, she was dragged along for more missions.