If you're starting from a New Game+, then it doesn't really matter, as fights on Insanity are easy but tedious no matter what you do, after level 25 or so. I personally found that outside encounters especially went faster as an AR adept/bastion, thanks to the variety of insta-kill options, and it's also a great build for starting from scratch on Insanity.
yeah shock trooper vanguaurd with singularity is the most powerful class to use. I had four new characters from scratch on insanity and i kept on dying a lot as well as my teamates and also had a very hard time killing them except when i started my vangaurd. This is the best vangaurd build if you wanna kick some ass even at low levels. All classes can survive and actually be a good class but if you want to kill your enemies very quickly use shock trooper vangaurd with singularity and get wrex and tali as your teamates.