I like playing support roles so this last round I went with Engineer, I've really been enjoying it especially because all the weapon certs are shared by light assault. Oh and so far those are the only two things I don't suck at.
I still haven't completely grasped how cert points are gained so I'm not sure if you could effectively spec multiple classes. For a while every time I logged in there would be 50 points waiting to be spent but lately they've been coming much slower.