Of the three you mentioned, I'd probably go with Fire/Shield. AAO with your AoEs can add up to some really nasty damage output. The SS/Dark could be good, but you'd have to be pretty careful about endurance, especially once you get rage up and perma/stacking. It takes a chunk out and Dark Armor just doesn't have the means to mitigate that.
My personal favorite has always been SS/Elec, though. Before I16, it was a very kill-or-be-killed combo, but since they turned Conserve Power into Energize? It's nigh unkillable (Tough/Weave really help the set, but then, they help all the sets, lol) and Lightning Reflexes means I inherently get KO blow and Footstomp up faster than other secondaries (well, SR can do that, too.)
Edit to add: AV and Pylon soloing? Perhaps you'd like Claws more, then. Not sure about how it plays on brutes, I've heard that some of the recharges were increased, but at least on scrappers it has the highest sustainable damage output, being light and fast and having 1-2 Follow-ups active at any given time. If not Claws, then I'd strongly advise Super Strength. Good mix of single target and aoe damage, but permarage, as well as stacked rage, can really put your damage output up there. My Stone/SS *tank* soloed AVs *before* IOs even came out. With a modicum of recharge added globally to the build, plus the fact that you can get more than 6 slots worth of SO values out of 3-5 slots per power, you should be just fine. Good Luck!
So yeah, I'd say go for the Fire/Shield if you are set on one of those three builds you listed. If you decide to deviate, give SS/Elec a try. Hell, I'm sure you have enough character slots to try both. 
~ WP
Just my opinion, feel free to disregard...
Fire/WP is going to be the toughest of the 3 choices. Fire/Shield is going to provide the most damage and with the right IOs will still be very sturdy.
SS/DA is an endurance hog and will probably leave you disappointed again.
Howdy all,
I'm getting back into the game after a hiatus (around the AE creation time) and I'm looking for a new brute. I have a 50 DM/Fire who I'm not happy with and want a replacement brute.
Here are some of my thoughts: Fire/WP, SS/DA (yay new patch, no longer cloud of smoke), or Fire/Shield.
I'll be gutting my 50 when the replacement can take all his IOs, but I'd also like a build that can get good performance without investing billions. My 50 has all of the health uniques and a few purples, and 100 mil. liquid inf.
Which of the listed choices would provide superior performance with the resources I have available? Also, if there are other powerset choices I should consider, please highlight them.
Thanks,
Carnal
Edit:
I'd like to engage in high-end activities, like AV (and pylon) soloing without inspirations, temps, etc. I'd also like to be able to be the team tank.