Man Utd were one of the biggest before the Sky money, they formed the traditional big 6 with Liverpool, Arsenal, Everton, Spurs and ourselves. (sometimes it was classed as the big 5 with us missing as we struggled during the mid/late 80's). Grand old clubs with the biggest stadiums, the richest histories and the fullest trophy cabinets. Those clubs grew organically over the years to become what they were.
Man Utd were skint in the late 80's, like a fallen giant. Big old stadium but looking tired. Yes, they have benefitted from the TV money massively, but most clubs have. Man Utd just happened to get to the top at exactly the right time to maximise and they got their by having arguably the greatest manager of all time.
I get what @BOF is saying. I'm a traditionalist as well and would rather have United over City.