Smash Juggernaut/Sweep Guardian.
More fun to play imho then Mara/Sentinel, ability to solo kill is pretty good and survivability is decent. Really fun class for Huttball, with Guardian Leap and Kick.
I have Sweep Guardian and Carnage Mara and both are nice in their own way and quite fun to play. Carnage Mara just takes lot more skill and timing to get it work properly, Sweep Guardian is lot easier to learn.