Any champion on Smackdown would be pointless. Miz has proven himself as a star on the number one wrestling show, Raw, why would he go down a level.
Once again, Miz cannot cash in on anyone but Raw's champion. He won the Raw MITB match, which means that his contract is for a WWE title opportunity, NOT an opportunity at any title, which is granted at WM's MITB, as it covers both brands. The reason why Kane cashed in on Mysterio is not just that it was advantageous, but because he was only able to cash in on Smackdown's champion. A lot of people on here mention hypothetical scenarios for Miz to cash in for the WHC instead, but that's not what he's allowed to do.
That said, I went with Orton. As others have said, Miz is not going to use the briefcase for a face turn, and cashing in would more than likely set up a feud with the victim. Cena is going to be tied up with Nexus for the foreseeable future, and I think they want to give the belt to someone else for a change. Both times he nearly cashed in on Sheamus, the crowd was going mental, and when Sheamus was given an RKO through the table at SummerSlam, everyone was chanting "We want Miz". Clearly, cashing in on Sheamus would do the opposite of what they want the result to be. Miz will eventually turn face, but not right now or any time soon. Ideally for WWE, they want him to gain massive heat from his cash-in and use an ensuing feud to push him further to the top and give him credibility as a deserving champion. After what they did with Swagger, I don't think they want to repeat that mistake. Putting Miz in a feud with Orton would be exactly what he needs and likely what Vince and WWE want.
In terms of when he cashes in, he won't do it at NOC. He will likely lose the US title to DBD, and from there, I'd like to see him face some main event talent on Raw and pull off some victories in order to rebuild himself the old fashioned way. I would like to avoid the possibility of Miz looking weak when he cashes in, and doing it after a loss will probably accomplish just that. We've got HIAC coming up in just a few weeks, which will likely give him a good opportunity due to the nature of what the WWE title match might be. There is also TLC in December, which would provide a similar sort of opportunity. Even if the cash-in is cheap, he needs to look good when he does it, and be able to back his reign up with solid matches that are more of what the crowd will have gotten used to by that point. Given that, I would like to see him hold onto the briefcase for at least another few weeks.
