I personally suck with the Assault ... a lot :P I find the Assault is best suited when enemies are directly in front of it. When jumping and weaving starts up though, it is in trouble, which is why a good, quick Huggable can outclass them. They don't have the consistant damage output like the Heavy does with its automatic weapons, which makes its slow speed even more troublesome. Yes, they do have massive damage, but if they can't hit you there's nothing to worry about.
I own the Assault, and it takes quite some practice to actually be good at it. The Assault's biggest weakness is EXTREMELY close range. You will just end up hitting yourself most of the time. His melees are also one of the weakest in the game.