The whole Moyes thing is odd to me. He may...may, possibly, grow into the job but there's nothing, and I mean literally nothing to demonstrate he'd be a good United, or even big, big club manager at this point. He's demonstrated he can work on a budget to an acceptable level for an upper mid table club. That's it. He's also never played very good football. Akin to O'Neil in that regard, who suddenly got proposed based largely on the fact he was close enough to British & got Celtic to a European final. Well Roy Hodgson and Schteve McClaren got teams without Henrik Larsson in them to the same European final. So what? In fact McClaren did so not too long after being Fergie's right hand man in the Treble season. Credentials that would surely put him well above all of them in the overly fertile romantic imaginations of many of the "right way" lot.
Both have always struck me as bonkers candidates.
As for the OP, at this point in time, Mourinho is easily ahead. If Guardiola finds managing the best team in the world, and possibly of all time, at the club he captained and grew up at too stressful to stay for longer than 4 years, then any criticisms of Mourinho being the more likely to bolt are similarly bananas.
Moyes, O Neil & to a lesser, but still tangible degree Pep are all based on a sort of pre-emptive romanticism. All the actual facts point squarely at Mourinho. In big shiny flashing neon letters.