I'm not going to restate opinions about the companions that have already been stated here. Assuming that Larian keeps a 4 person party, I'll base my choices on whom I'd quickly replace if/when someone else comes along.
Laezel - I use her because she makes the most sense as a tank in the EA. I don't particularly like or hate her, but I always feel that I'm the one that's replaceable when someone better comes along. I love what she brings to the party as far as combat and her jumping ability goes. But when I can replace her, I'm pretty sure she's gone unless her story takes a different turn. I might not tell her to leave, but if there is someone better, she's unlikely to get much party time.
Shadowheart - I generally like her, but she is in and out of my party as necessary whenever I need Gale or Wyll instead. I wonder if her personality is affected by whatever is hiding her memories as well. Like others, I believe she is a Selune disciple brainwashed to believe she is a Shar follower. I most likely will keep her in my group the entire game.
Asterion - I generally dislike him, both because he's a vampire and because I don't see Rogues and the like as so prissy. I use him in my group mostly because my playstyle uses magic less and combat tactics more and Asterion makes a good scout and ranged specialist. When someone else comes in I like better (probably Haslin because Shadowheart can take care of locks). I'll replace him and tell him to leave.
Gale - I generally like Gale. My opinion of him mirrors what Niara has posted. I will keep him my group and will play him as necessary. Since I'm not exactly sure what class my MC will end up being, he may be more of a camp follower and sometimes party member or may always end up in the group. But I generally like his character.
Wyll - Just never warmed up to Wyll. I have a bit more sympathy to him I guess than many here, but his character class is just one I struggle with. I do like a good redemption story, but I'm just not sure Wyll IS one. He's a Hero wanna be and seems just too defensive of his actions. If Larian is reading this, maybe they can do better with him. But for now, probably will rarely use him as a party member and he'll end up being a camp body or I'll tell him to leave.
I like the theory about Shadowheart, that makes her a little more interesting, although I don't like her ability to pick locks as she is a Cleric and that is usually attributed to rogues or rangers. One thing I will say is, I noticed a lot of people here in the forums who don't like Astarion give the reason of not liking him for being a vampire. I'm curious to know why is that an issue? The majority of vampires that I have read stories on, usually behave the same way. Some may think it's cliche but I think the reason why they are written like that is because that is the most recognizable trait of a vampire. They are seen as extremely seductive, some are bi-sexual like Astarion, and sassy but they also can take a different turn very fast depending on a circumstance.
