Plus if you're doing a king-of-the-hill objective, running is counter-productive, since it will just cause you to lose. You either hold the location you're told to - with missiles if need be - or you may as well just give up and die.
Adept: Human, Asari, Ex-Cerberus, Asari Justicar (very rarely).
Engineer: Human, Quarian, Salarian, Male Quarian, Demolisher.
Sentinel: Turian, Batarian.
Vanguard: Human, Krogan, Ex-Cerberus, Slayer.
And there's still the Geth Engineer, three N7 classes (all but the Destroyer), and a good number of classes released or to be released from the most recent DLC (the Volus, Krogan Shaman, and pretty much everything else from the above four class categories) that I'm interested in.
Edit: I'm starting to think that the developers went a little overboard with how many Dragoons they send at you in the extraction waves. I just had a game where my team got swarmed by about a half dozen of the things in rapid succession. That in addition to the usual troopers lumbering about, including Atlases. We took them down with about as little trouble as possible (two of the team were using Harriers, which somehow seem not to have been nerfed since I last played, and I was doing fairly well against them as my Turian Sentinel with Warp and my Phaeston with damage and piercing mods), but it got very chaotic there for a minute, and had we been in a more exposed position we could've been in a lot of trouble. And this on silver.