So exclude Lae'zel, exclude Shadowheart - who's left for romance when you're playing a honorable character? Only Karlach, whose good ending is sacrificed for the sake of a cheap tearjerker.
All of them - except Minth and Ascended Astarion probably - but what's the problem with Karlach? That you have to join her in Avernus? That's is not looking terribly favourable on your stance on loyalty.
I would follow her if there were a reasonable case for it - like saving her or convincing Zariel to free her. How can I defeat such a powerful brain, yet somehow I can't "buy" Karlach from Zariel to let her periodically visit Avernus and restore her engine? Following her just makes me feel like I'm being sacrificed for a tearjerker moment. Plus, I'm not exactly into two-meter-tall red women with horns and tails.
