Unlike at various points in the past there are no truly outstanding candidates available - you don‘t have a pep or klopp carrying out a sabbatical and waiting for the right offer to come along.
The choices therefore lie between a more experienced manager who might stabilise things for a period like an allegri (if you’re willing to put up with cagey, cautious, highly tactical and somewhat old-fashioned football which involves grinding out results consistently) versus a younger German alternative who is tuned into the current tactical zeitgeist of high lines, aggressive press, vertical play, 4-3-3s, inverted wingers, high fullbacks, keeper sweeping behind, etc.
Pochettino’s style is difficult to define for me. I don’t think he’ll suddenly transform his record of having not translated periods of pretty play and consistency into actual trophies when he’s nearly 50. He’d certainly be an improvement on ole, but whether he would take united any further than he took Spurs remains open to debate for me.
If I was a united fan, I’d be targeting nagelsmann and then giving him time, editorial independence and resources to see if he can build something. There’s always a risk he could turn out to be like BR at Liverpool or AVB at Chelsea, but I wouldn’t bet against him transforming himself into a klopp type figure. And the football would be excellent to watch.