Shadowheart. My kindhearted main char wants to save her from the bad goddess. And of course sleep with her. Not sure what has priority ... (that's a lie)
It doesn't hurt that Shadowheart is of the strongest class, too. From the rest Gale is always in my party, I like him. Wyll was the third companion, but I was more fond of him when he was the dubious hero of the EA. Now that he is a real hero I lost some interest. I don't like nobles and horns too, so maybe he will be replaced as soon as I get another companion with a minion (Minsc? I'm not sure I like him, let's see). The rest of the companions I ignore.