I haven't let anyone die in any of my playthroughs, mostly because I'm a total completionist.
Squad setup for my first playthrough:
Technical Specialist: Tali. I wanted to slap Jacob when he was like, "I'm perfect for this!" You have all the technical skills of my dog. No.
Leaders 1 + 2: Garrus. Didn't even need to think about it. I freaked out a bit when he looked like he was going to die after he got shot. Don't scare me like that! I almost hyperventilated!
Biotic: Samara. I didn't need to think about this one either, but I did want to slap Miranda. Partially because she was stupid enough to think her genes made her perfect for everything, and partially because 'everything' included keeping my team safe from the evil bugs. Newsflash, Samara (and Jack, but I was afraid she'd drop the shield in order to kill things on my first playthrough)are better than you are at it. DEAL WITH IT.
Escort: I think I picked Thane because he works well alone and I figured he'd use his assassin mojo to kill everything. Mordin would have been better, but oh well.
Final Team: Garrus and Mordin. I didn't realize then that picking Mordin probably saved his life, and that Garrus probably should have stayed to keep the squishies (Tali, Legion...) safe. I pretty much just lucked out on this one; I was focused on blowing crap up instead of tactics at this point. Go team?
I had all the upgrades and finished all loyalty missions (except Legion's, but I finished his loyalty mission before my crew got taken) before I even messed with the derelict reaper; I figured it would start something important, like endgame. Bioware, I love you, but you're predictable.
I immediately grabbed my superhero cape and rushed off to save my crew first chance I got, because I wanted my snarky engineers and drunken doctor back. My thoughts on Kelly were, "Oh. Hm. I guess we can save her and the other crew members too, while we're there. Engineers and doctor first, though."
Yeeeeah, I'm a terrible person.