Allen is more ready than Grier. And if you have an investment (doubtful it endures) in Grier you could ruin it by throwing him to the wolves.
Therefore I am about Allen as the next in line, but not right now. You have to go two or three more games at least to give Cam a chance to come around. If he does not show any potential for a return to form, maybe Allen can win us a game or two.