This is a wrong question. The right question is to ask "how many of our players are in above mediocre form"? Because most of them were above average talent-wise at some point, otherwise they wouldn't be in the team, however how many are this season - is a completely different matter.
Case in point: DDG used to be world-class, but this season he IS mediocre, he is worse than mediocre and has been such since the end of last season.
Now if you ask the question about the form, very few of our players will qualify.
Maguire, AWB, Martial and maybe Luke Shaw are the only ones you can definitely say they are in above mediocre form since the season started. Rashford is close, but if he was in good form he should have destroyed Crystal Palace and Wolves. And he didn't. So...
Another way you can ask this is - which one of our players would make starting positions at Liverpool or City, this season? No way DDG or Pogba are making that list. DDG because he's just horrible this season, and Pogba because he's way too inconsistent.