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?