Blake can't play. If that's all we can get, I'd stay with Miller.
It is not like we can just say that, Miller is unrestricted, so he decides where he goes. The team does not want to give him more than two years and they would be lunatics if they give him a three year or longer deal. For two years at the right number I am fine with keeping Miller.
Blake can play, although he is more of a complimentary, quality back-up level PG. He is a good shooter from distance, careful with the ball and no worse defensively than Miller. Not much of a threat to drive to the hoop, but if Holiday develops quickly, he is also less likely to bitch about accepting a more limited role. Plus he is cheaper, giving them some room to acquire another shooter.