Who is best, Jaheire or Keldorn? Do you get to keep them both? Do they have any quests?

I would say it depend on the rest of your party members.....but.... i think Jaheira is the best. You can always get a fighter that is almost as good (or even better). You can also replace Jaheira with Cernd, but Jaheira is something special! i use them both in my party.

Depends on how many frontline fighters you already have. Keldorn is mediocre when you first get him but there are weapons you find in the game that will turn him into an absolute tank (you probably already know which ones but I don't want to spoil you if you don't). Jaheira can also be buffed out but not as much, the flip side is that she has healing spells and Keldorn being an inquisitor doesn't. Your choice but personally i couldn't go past Keldorn.