I'd rate them in this order:

1. Laezel is the best. She's written well. Her personality is solid, and she makes sense. It's painful to see how she's treated when she comes across the other githyanki, and one thing I really appreciate about her is that if you play a githyanki as Tav, your character's creche didn't teach you any of the purification stuff that Laezel talks about. So whatever she's getting at, it's unique to her creche.

2. Wyll is next. I hate his stats, but as a written character, I like him. I like his story, and I like how complex he is as a person. He sold his soul to be a hero, and it's clear that being good is important to him, but he's okay with lying, and when pushed, he's willing to violate his own sense of right and wrong to torture another person. To me, he feels like an intrinsically good person who's unfortunately addicted to something bad, which happens to be Mizora.

3. Shadowheart. I put her at number three because I can't be 100% sure where her story is going in regards to her missing memories. Right now, she plays her role very well in the party, but if it turns out that she's legitimately an evil worshiper of Shar, well, that's not coming across. At the moment, she seems confused, but with a goodness buried deep down inside of her. She's secretive yes, but almost in an innocent, immature way. If her story ultimately backs up all of this nuance, then wonderful, she climbs the ranks into one of my favorites.

4. Astarion. I don't hate him. Overall, I like his character well enough. It's just that I don't know enough about him right now. It's also difficult to trust him. He does his job as a rogue well enough, but I want to learn more about his background.

5. Gale. The absolute worst, no contest. Not only does he eat valuable magic items, he also comes to the table with a ridiculous, outlandish story about having a love affair with Mystra. I would prefer the characters to be a little more grounded. His backstory is, in my opinion, overly try hard. I appreciate that other people feel differently about him, but for me, I just can't get into his story or take any of it seriously.