Interestingly, only Astarion and Minthara have lot of fans in Internet.
Gail, Will, Laezel, even Shadow Heart (although she is cute and mysterious) seems to be chosen by many in game, but they do not have enough charisma and charm to have many discussions about them. They are good companions, interesting personalities, the developers did a good job but just ... just not that.
Creative people like bright, charismatic and self-loving maniacs who have a difficult fate and who know how to inspire
I'm on the record saying that Shadowheart is the most interesting companion to me so far, probably the best written too. But the Shar/Selune speculation threads are long fallow now. People enjoy discussing morally compromised characters, and more, how they feel they're being treated by the game.