Depends on the mission and game.

In one I almost always had Tali on my team with the third member being whoever I felt like at the moment.

In two I try to use everyone but usually lean towards Garrus, Tali, Legion and Samara.

In three again tried to use everyone but leaned towards Garrus, Tali and Javik.

Overall favorite as far as backstory personality etc I'd probably have to go with Tali.