Raphael and Gortash would be my picks, but since it's companions only, I picked Astarion.

Second choice would've been Halsin.
Honorable mentions to minor characters Rolan, Abdirak, and Rugan for other favorites. RIP Rugan's cut content; we'll never get to have those drinks together. That's where imagination comes in, I suppose. Abdirak had a lot of potential as well! Surprising they made a one-off character so memorable. The game really could've been something
spectacular if they'd gone at the remainder of it with the same gusto they had with Act 1 and some of 2, and maybe they did once, but I understand abruptly having to rewrite the bulk of the story is going to have a serious impact on the whole project. At least Rolan got his conclusion, lol.