I have both BS/SD and SS/SD at 50 and both are very fun to play. The only big difference that I see with /SD for Brute is that Shield Charge as a damage cap of 400% so the Brutes will do way less damage. With a Brutes Fruy and AAO and the slotting in the attack it will be close if not at the damage cap. With my Elec/SD brute I don't even need to hit build up because it doesn't help 
But still SS/SD is a blast to play and one of my favorite toon to play.
"All right, they're on our left, they're on our right, they're in front of us, they're behind us...they can't get away this time"- Chesty Puller US Marine Corps
AaO is about twice as effective (relatively speaking) on a scrapper, and Shield Charge is about 50% stronger.
SD doesn't hit any scrapper cap on resistances and doesn't heavily relies on regen, so the slightly bigger base HP brutes get doesn't make a big difference.
That said, it still remains one of the strongest if not the strongest secondary available to brutes, so you can't go wrong with it, especially if paired with SS.
Well, I love brutes and scrappers both and I know that /Shield is much better on a scrapper because of the higher base damage, but how big is the difference? I am leaning towards scrapper BS/Shield since it is so simple to soft cap, but brutes also have Super Strength and I like thinking about rage+SC+FS. Any suggestions or comments are appreciated! TYVM!
"I have always been a fan of science fiction. It all started when my parents forced me to go to church when I was a child."