In terms of fanbase, trophies, history and players. I think most of us can agree the top 9 should look a little bit like this(in no particular order):
-Real Madrid -Barcelona -Bayern Munich -Liverpool -Manchester United -AC Milan -Inter Milan -Juventus -Ajax
But who would you place to make it 10? Maybe Arsenal, Benfica, Chelsea, Porto, Man City, PSG? Maybe a South American club? Who do you choose?
1 Real Madrid
2 Man U
3 River Plate
4 Flamengo
5 Liverpool
6 Inter
7ACM
8 Bayern
9 Barcelona
10 Boca
HM Palmeiras, atlético Madrid, the Montevideo guys for their history
Bayern, Barcelona, Liverpool, and Milan are all bigger clubs than Man United.