I was thinking about going through as my Operative/Infiltrator on Insane, but as of the last 2 story planets on Hardcore, my tech mines weren't doing nearly enough damage and not enough CC to warrant their usage *which sucks because the Operative talents increase those skills*.
I'm going through now as a female adept with AR, or Vanguard with electronics (for the shield boostage). Liara tore shit up during my Hardcore run, and made even colossi a non-issue.
Warp seemed to be the make or break skill for long fights, as the damage boost really helped. I see all these people on the official forums saying that the only way to play insane is with a Soldier who spec's Adrenaline/Immunity-- but I don't think I need to live that long if I can kill stuff 90% faster with no cool-down.