You defiantly need to look at what the rest of the league and Europe were like when United and Liverpool were in their prime, United used walked the league because of the lack of a challenge, Liverpool also had few challenges in their prime, No top 4 in when Liverpool dominated Europe, United was poor early champions league and its format
Cup's are hit-and-miss and and really should be low in value and most of the big teams see it as a last option if they are not doing well in the league,
I am not saying it because I am a Manchester City fan, But City really have to play the system first and then try and win silverware, Plus, we are talking a whole new ball game in the modern game with VAR.
I don't do the greatest team because of time and place in football era, But if your asking Right here Right Now then its a easy question MANCHESTER UNITED hahahahaah