This is the so-called TK, or Tatekwaki Kuno Dilemna, oft paraphrased as
"I cannot choose! I must have both!" What I've done on my run-throughs is to remember my alignment. If I'm evil or neutral, I just add Imoen for a moment to free her, then drop her: the least I can do, since she helped me in the past, but that's it. If I'm good, I of course keep her: she's my sister, and an old friend: I couldn't abandon her!
As to whom to leave, what's your current party?
Ah, but you're the GameBanshee Hater: almost forgot. Maybe you don't want to deal with us; quite a few of us also post over there.
[ 01-24-2002: Message edited by: fable ]