I don't think we know what either if them is, but the Bills think highly of both, and their process seems to be working okay so far. I don't see any reason not to be optimistic.
McCarron was 2 - 1 with the Bengals, and should have been 3 - 0, except the Bengal imploded.
https://www.cbssports.com/nfl/news/bengals-have-playoff-meltdown-for-the-ages-vs-steelers-5-things-to-know/