My squad usually consisted of my favorites - Miranda & Samara being the two female mainstays because... well, they're nice to look at and all and with the impending Reaper/Collector attacks it seemed fitting to have a nice view.
I also regularly rotated in Garrus as he's just a likable Turian. Grunt & Zaeed were also used regularly b/c of their combat powers.
I play as a soldier normally, so I really like to have a heavy hitter and a lightweight biotic with me at all times. I like to choose Garrus, Wrex, Grunt or James. I also choose Liara, Miranda, Samara or Jack.