If I had to choose: Lae'zel and Gale
Lae'zel because I enjoy roleplaying as slightly-dumb (or naive/brainwashed) fighters who eventually realize something that shatters their world.
Gale because it will be interesting learning about and solving his problem from his perspective, along with possible future interactions with Mystra.

SH and Astarion would be fine, but I'll never do enough playthroughs to make it past the 1-3 Tavs, Lae'zel, and Gale.

Never Wyll. Wyll's a filthy liar and way too full of himself considering his actual skills.