Giggs claims Manchester United's treble-winning side of 1999 are better than both teams.
Giggs, a 13-time Premier League winner, said: "I'm going to say they wouldn't have beaten our United team, aren't I?
"We had great sides in 1993, 94, 99 and 2008. But the best was 1999 because of what we achieved."
But the 45-year-old admits he enjoys watching both of the Red Devils' historical rivals.
Giggs added: "They are two fantastic teams. Liverpool, the comeback at the weekend and City are still playing the same way, not changing, even though they didn't have a shot on goal in the first half against Southampton but they had the confidence to trust themselves and show fantastic composure and quality.
"They are both brilliant teams who, unfortunately I do enjoy watching."