You should get a Dire Wolf. But since they're not around yet...
The Centurion-9A or the Hunchback-SP would make good choices, if you want to try a lower weight class. They're both two of the best brawlers in the medium weight class, and you should expect to see a ton of them when CW arrives.
The Jagermech has a ton of brawling options as well, especially the Firebrand.
The Orion is basically an assault mech in its own right, and I'm sure that most people would say the Orions mostly better than the Awesome variants, which all suffer from low armour for an assault mech and a being about as big a target as an Atlas. I generally prefer medium and heavy mechs to assaults mechs, but if I had to pick a in-your-face in-the-thick-of-it brawler mech, I think I'd choose the Orion.
You could also take another Atlas. master the basic efficiencies for two more and you unlock the elite tier. Mastering all three basic efficiencies will double their usefulness, so say heat threshold increase from 10% to 20% I can't make a recommendation as to which ones to take, but the only real reason to take the K is for double-AMS, so you might be better off with the D and RS. The Boar's Head also just released yesterday, and I have to say, if I had to pilot an Atlas, that would be my preference. three energy hardpoints to each arm, a ballistic in the right torso, and missile in the left, and an XL400 engine (which could later be put on a Battlemaster for moving at 84 KPH with the speed tweak).
P.S. Get a Dire Wolf when they come out. Easily my favourite assault mech, I've loved piloting it in every MW game I've played, which may not sound like that much to you, but it does mean a lot once you realize that I generally hate being in anything slower than 70 KPH.
Edited by MarsAtlas, 02 October 2013 - 07:34 AM.