In my experiences playing brawler, my best setup is Piston Punch, Burning Drop Kick, Ultimate Uppercut and Feint Jump, but in terms of a overall MU spread, I don't think what I run with is the best.
Feint Jump is a no brainer, no other down-b compares.
I run Piston Punch because, while the recovery is very linear, you have Feint Jump and Burning Drop KIck to cover that, it really shines as a overall kill move, especially on stages like battlefield, where if you are on the top platform, which I know is situational but still, it kills very early and maybe even at 0% against the lightest characters, I'm not sure. Piston Punch isn't too bad out-of-shield either.
Burning Drop Kick is interesting because while I don't think it has as much offensive potential as Onslaught, it's not bad as a recovery since you aren't put in special fall. This pick is swappable with Onslaught, though.
Ultimate Uppercut is a good surprise kill move and with the super armor, granted it doesn't come out immediately, it can eat a lot of attacks. Don't try and use it all the time though, I learned that the hard way multiple times...