Whether this one or that one would be a good fit at United depends entirely on whether we want to keep our model - that is, a manager who is responsible for much more than what is required of most managers.
If we were to adopt a new approach and go for someone who isn't expected to follow in Fergie's footprints as the great overseer of the whole United monster, there are several candidates out there. I think Ancelotti would do well here, based on nothing much beyond him being a clever bastard. But if he were to get the boot (which could easily happen knowing those people) and we were to alter our basic approach, I'd like him here more than most names people wave about at the moment.
If, however, we want to employ a manager who is to be in charge of the whole club, top to bottom, Fergie style (or at least close to it), the list is much, much shorter. Some years down the line OGS could be a good candidate.