Then, Gale and Lae'Zel. They're good. They fit within the main story really well. In act, without LaeZel the whole main plot falls flat on its own face. They also don't come with an over-the-top 'designed for a certain audience' syndrome, making them a little more natural.
I have run a playthrough without Laezel or doing the githyanki questline. It mattered little when it came to the main plot. Tbh, I'd not bother to recruit her anymore, since I suspect it is the same when it comes to not having Laezel in the creche.
I think the only companions that have any real impact are Gale (additional endings) and Shadowheart (you cannot chose the evil path end of act two without her in the party).
