I like McDaniel and Shanahan. Would rather give it to the coach of a great team than the coach of an averageish better-than-expected team. And SF and MIA are the two great teams who seem most dependent on their coaching, with great designs to both offenses and other good signs about how they do the rest of their jobs (like that McDaniel video).
HOU & IND both fall into that averageish better-than-expected category that I'm not as excited about. IMO Detroit is too close to that too, despite their 10-4 record, as seen in their not-that-great point differential (+51, vs. +147 for MIA) and their not-that-great Super Bowl odds (+2000 or so, vs. +850ish for MIA). Really just SF, BAL, DAL, and MIA who meet the bar of "great" and not underperforming.
McDaniel is the more exciting pick, with the innovations on offense, all the
big plays, and some of the better-than-expected juice. I've been paying more attention to him than any other coach this season, basically all of it positive, so he was my gut choice first pick when I saw the question and the guy I cast my vote for.
Much of the "Purdy for MVP?" discourse is an argument for Shanahan as coach of the year, with all talk of guys schemed open and the ease of producing big numbers in that offense. And really it's a point in favor of Shanahan that people already had the Niners pegged as one of the top teams in the NFL back in the offseason before it was even clear who the team's quarterback would be. And then the team turned that huge question mark at the most important position on the field into an all-time great season at passing efficiency, so there's some better-than-expected juice here too along with the expected strong performance based on a years-long track record. After thinking through it to write this comment, I'd change my vote to Shanahan 1st and McDaniel 2nd.