Which of the three is the worst signing ?

Maguire had two great seasons. Until August 2021. Sancho and VDB haven't shown anything.
Maguire was hardly great for his first 18 months. He was fairly inconsistent with some great matches, some shit matches, and overall averaged out to being 'decent'. It was 50/50 between him and Lindelof, with the latter not having as many great games but also not having as many poor ones, so overall they were a similar level.

It was only in the second half of his second season where Maguire was 'great'. Full credit to him during that time, it looked like he was stepping up to be the defender that we hoped we were buying and he'd continue on like that in the future. Unfortunately it turned out to be the exact opposite when the next season started and he utterly collapsed as a player.

That decent 18 months and great 6 months does put him ahead of Sancho and VDB, but saying he was 'great' for that entire time is going significantly overboard.
 
At least you could see how Sancho should theoretically have worked out. So regardless of who might look like the worst signing in hindsight, I will throw the transfer process a rare bone on that one and say it was still the right decision to sign him at the time.

The VdB one was just daft. And can't believe people are writing 40 mill off as "cheap". Here we are a few years later scrabbling round down the back of the sofa for some change to see if we can bring in a much needed midfielder and then having to settle for a loan. That's what years of iterating on VdB-level transfer decisions gets you.

Maguire was a massive overpay and form fell off a cliff but he's also a victim of getting an unshakeable Titus Bramble rep in the meme age.

At his best Pogba was absolutely light years ahead of any of them but there's something inherently cringeworthy about signing back your own player at an enormous premium who you originally released on a free. Then releasing them again.