It's tough to judge now. We'll know couple of years from now.
Donny Van de Beek has barely played , he's actually barely a footballer, totally invisible on the pitch. Pretty limited both technically and physically(athletically). But, his wages aren't too high I think(lowest of the 3 mentioned in the post), and he is showing willingness to leave(even permanently, not just loan), so there's that as a positive with him, I guess.
Harry Maguire is a footballer(contrary to Van de Beek), but still a terrible one. Has shown arrogance, greed, narcissism even. Not willing to reduce his wage and move elsewhere where he could actually play and he prefers sitting on the bench for two more years and collecting paychecks. Harry is actively sabotaging the club, we couldn't bring another, competent CB by selling him first. But, I also understand his position - more money(wage) now, over dignity and playing football. He is entitled to it, I guess, the club has given him that contract because of absolutely shambolic recruitment/scouting(Woodward).
Jadon Sancho is a lazy slacker who is talented, but doesn't lack the competitiveness, work rate and drive to succeed as a footballer. I don't think he actually likes, enjoys playing football that much. It's just a job which affords him lavish, luxurious lifestyle on a very fat paycheck. Situation right now is tense with the manager, disciplinary issues are a big problem. If we manage to ship him to Saudi somehow in January(or next summer) for decent amount of money(at least £30-40m), the whole problem will be somewhat resolved and he will just be forgotten as a waste of talent. I think he is money driven and that Saudi transfer is possible. He can't wait to gather some serious money, and then buy a house and retire somewhere in Florida, Bahamas, Jamaica, Spain, French Riviera, California etc. and enjoy the rest of his life in a very hedonistic fashion - parties, beaches, girls, alcohol, drugs, travelling, video games...whatever.
All things considered, I think that Van de Beek is the worst footballer amongst this infamous bunch and a very pointless signing, but Harry Maguire is the worst signing considering the fee, wages, his arrogance, greed, behaviour, unwillingness to leave and just sabotaging the club as a circus clown/jester when the whole world knows he's not good enough to play for Manchester United and he's mocked into oblivion worldwide and became a meme forever - symbol of United's decay, Glazer Apocalypse. From Rio Ferdinand and Nemanja Vidic(best CB partnership in PL history) to Jacob Harry Maguire. From Mount Everest to Mariana trench. Jesus Christ...
I understand Maguire's greed, but he's really gone on my nerves and can't wait to see him get out of the club(it will take two years, unfortunately). He could become the Man United player I hate the most(in United's whole history), not counting criminals/delinquents like Greenwood.