It astonishes me that y'all are surprised people choose Garrus and Tali for the final mission. Sure, they're not as handy against the collectors, but they're the favorite characters for a lot of people, including myself. If they were real, I'd consider them both close friends. Of course I'm going to take my friends into the final fight with me, especially since even on the hardest difficulty, the final battle isn't all that hard, even with ill-suited squad mates.
Anyway, on my first run, I did everything right except that I sent Grunt back with the crew, because I thought they'd need an escort who'd be able to deal with large threats on his or her own. Grunt obviously fit this description. I took Garrus and Mordin with me to the final fight. That, unfortunately, meant that at the final segment, my crew was lacking one of their strongest assets.
Because of that mistake, Tali was lying dead somewhere in the collector base when the bomb went off >_<
Needless to say, I subsequently started another play-though.