This is my CTF-3D brawling build I came up with which I run when I don't feel like sniping. The STD260 is a little slow, though its enough to stick with your assaults. It's great for either shooting over ridges, or to pop up from behind your front line and drop AC20 rounds on your targets' heads. Works great in a straight-up brawl as well since the JJ's give you a faster turn than most other brawlers. Anyways, here's a screenshot of what this guy can do in the hands of a mediocre casual player. I am cherry picking here since, while this isn't my highest damage round ever (probably second highest), it is the most kills I've ever gotten in a match.
Avoids heat tax, has decent armor, jumps. Pretty groovy 'mech overall. A bit slow for my tastes, though.