Honestly, I think the Origins system is eating up a lot of those resources, particularly in regards to the comparatively low roster of companions. Try playing a cleric of Shar, or a Githyanki . Hard to not get the feeling you are playing second fiddle to Shadowheart or Laezel.
As for my favorite companion, I'd have to go with Shadowheart. Not only is she a Cleric, which is really, really useful in-game both mechanically and with the large number of magic items that synergize well with healers, but she's also the one seemingly most directly involved with the plot of the game, what with her puzzle box and the emphasis on Shar v Selune in Act I an all that. But most importantly, she has way more dialogue than any other companion as far as I can tell. That helps a lot in getting attached to characters.
