Well for 'MMA BJJ' as you call it, I think that fast, aggressive jiu jitsu/grappling is most effective, because most of these wrestlers just won't see it coming. Not many can just throw crazy submissions from nowhere like that, but spend too much time trying to set things up and the wrestlers will just beat on you and tire you out.
For example, Rousimar Palhares can have submissions set up before the fight even hits the ground, he may not always showcase minutes of grappling beauty but he's setting up all the time, and the submission rarely fails. And it's usually within the first 2 minutes.
For MMA, I think that's the most effective Jiu Jitsu, especially with all the grinding wrestlers - they won't go for takedowns so often if they think they'll land in a leg lock.