which one of these toons would you pimp out?
None.
Of those I'd lean towards the SS/Shield Brute. Good survivability, good aoe damage, good single target damage, +to hit for higher conning foes, good soft control. But the best advices I can give is the one that you enjoy playing the most. Expensive IOs won't make a hero you don't like much into one that you do.
@SBeaudway on Pinnacle, TaskForce Titans Supergroup.
The Spines/Fire and SS/Shield would be awesome combos to pimp out for your stated purpose. Or you could combine them and make a SS/Fire to get the best of both worlds. I think the best bet is to narrow down what you want to play, then ask about how to IO that specific character.
The SS/Shield Brute.
The Spines/Fire doesn't have a taunt aura, which makes farming a little bit annoying.
For speed farming the SS brute is probally the best but for all around slaughter I'd go with the DM/SD scrapper
The more people I meet, the more I'm beginning to root for the zombies.
quite like my wp/dm tanker - it can handle x8 spawns quite easily, only downside atm is its not exactly fast at taking them down, but then I haven't quite finished pimping her out yet.
http://www.scene-and-heard.com/cov/covsig.jpg
SS/Shield Brute or Spines/Fire Scrapper.
I have a fully IO'd spines/fire. It doesnt really impress me. Against Demons, it does good but other than that, blah, imo.
I'd go with the DM/Inv. Of your choices. Or SD/Mace for the other of yours. Im working on one of those atm. May want to try an Ice tank. I don't see many of those. Im gonna go with Ice/Kin melee after the SD, just to try it out. SnL and NRG are looking easy to cap.
SS/Shield Brute
Footstomp + Shield Charge = Happy Dance of destruction.
BIOSPARK :: DARKTHORN :: SKYGUARD :: WILDMAGE
HEATSINK :: FASTHAND :: POWERCELL :: RUNESTAFF
An ice/fire tank,tho thats cos i pimped mine out :P
It doesn't cost a lot to be nice and reply to tells

DM/Shield Farming
Let this help you decide about dm/shield scrapper.
( Link to youtube. )
You mentioned Mace so I might go with a Mace/Shield Brute. Not really in love with your existing options, to be honest.
The City of Heroes Community is a special one and I will always look fondly on my times arguing, discussing and playing with you all. Thanks and thanks to the developers for a special experience.
....for x8 spawns solo and general farming and all around +4 carnage (believe it or not I am bored with the teaming now lol).
I have a
spines/fire scrap
dm/shield scrap
fire/fire blaster
bs/shield scrap
dm/da scrap
dm/wp tanker
db/inv scrap
ss/shield brute
i am considering making a war mace + something also.
as you can see I don't have many brutes but am defintiely considering making some more.
TIA!