The Dutchman believes Liverpool will go all the way but he wants Manchester City to win.
Manchester United pulled off a miracle against Paris Saint-Germain in the last 16 to make it to the quarter-finals.
And their reward was to draw Barcelona in the last eight.
Van Gaal does not think the Catalan club are the best team in the competition despite the extraordinary talents of Lionel Messi.
He told BBC Sport: “People think Barcelona are the best but they are not.
“Manchester City and Liverpool are more of a team than Barcelona – and Liverpool are more of a team than City.
“In my philosophy the best team shall win but I hope for City because they play the best football.”
Liverpool reached the final last year only to be beaten by Real Madrid after Mohamed Salah went off injured early.
Van Gaal also revealed he could have chosen Tottenham over United when he was offered the manager’s job.
“Tottenham were a better selection because Manchester United were an old team and I knew I would have to transform them,” he explained.
“Was it the wrong choice? Maybe, but I follow my heart.
“I worked at the number one team in the Netherlands, Germany, Spain and now also in England.”
Liverpool take on Porto while City take on Tottenham in the quarter-finals of the Champions League.
The other match sees Juventus and Cristiano Ronaldo face off against Ajax.
United return to Premier League action on Saturday when they host Watford at Old Trafford (3pm).