My first playthrough, I lost Butch, Agent 47, Robocop, and the Cockroach Doctor. I had went into the playthrough completely blind because people who went and tried to play the game whilst looking after everyone so they had the "perfect" storyline was lame. How is that even fun?
It was a much more personal story, and by the time Shepard has to give his little speech, it meant a lot more to me.
The second playthrough, the one that I'm probably gonna use for the next game, I only lost Mordin. For some reason, everytime I send him into the vents to clear the way, he always gets blown away in the cutscene following it.
It was weird, because Miranda's a ***** and wasn't loyal to me because I took Jack's side. She still managed to survive.