The Dutchman returned to action on January 16 after a traumatic Christmas during which his wife suffered a brain haemorrhage.
The 39-year-old was in good form in last nigth's League Cup semi-final second leg victory over Manchester City at Old Trafford, making a superb save from Micah Richards in the second half.
United have not conceded a goal in the Premier League since his return and Ferguson is delighted that he is back in the side.
"Edwin makes a big difference," the United gaffer said, according to Press Association Sport.
"I know there are a few young keepers out there doing very well but Edwin is the best in the league just now.
"It is not just his saves, it is his composure and use of the ball. It is good to have him back."