Miz winning could get them Miz v Bryan for the belt at Summerslam, which is a huge match for exactly the kind of crowd that going to be there. I think that's where they're going.From a story standpoint, Joe/AJ makes the most sense.
I wouldn't put it past them to go with Miz though, given how thirsty WWE is for mainstream coverage. With Miz and Mrs. about to debut, they might want to put a bigger spotlight on him.