My main Shepard is an Adept, so tech companions are more useful to take out to complement my biotic powers. In ME2 Mordin is surprisingly good to have at your side, as is Tali, and I found in ME3 I used Kaidan and EDI a lot.
I also liked Tali in ME1 & 2, but you get her too late in ME3 to be of much use, much like Legion in ME2. Garrus is great from start to finish, naturally.
I did actually like James and found him very useful. In ME3 I often went out with him and Kaidan at my side.
So anyway, top 6:
Mordin
Tali
Kaidan
Legion
Garrus
James
I also liked Tali in ME1 & 2, but you get her too late in ME3 to be of much use, much like Legion in ME2. Garrus is great from start to finish, naturally.
I did actually like James and found him very useful. In ME3 I often went out with him and Kaidan at my side.
So anyway, top 6:
Mordin
Tali
Kaidan
Legion
Garrus
James