I have seen so many silly top 10s on the Internet regarding this topic, including one made with AI, and some of them are absolutely ridiculous, putting even PSG or City over teams like Milan and Inter for example.
There are nine clubs that are sacred for the sport and should not ever be left out of any historic top 10, regardless of the order in which you put them and those are Real Madrid, Barcelona, Bayern Munich, Liverpool, AC Milan, Manchester United, Juventus, Inter Milan and Ajax. And no other team in Europe(and frankly, the world), is bigger than any of them.
After those 9, put whatever club you want, put a Portuguese one, or Arsenal, or Chelsea, or whatever. But those 9 are non negotiable and leaving them out honestly makes any top 10 look either ignorant or made by a really young person.
Edit: And I mean big as in overall trophies, status, prestige, players, ballon d ors, history, fans, etc. Not just followers on social media and revenue.
I don’t care about this sort of list but what’s funny is that the newer batch of the “red” club fans who think bandwagoning these historic clubs give them a moral superiority over those who chose “blue” clubs for whatever reason. At the end of the day they’re just fellow glory hunters who do not even live in the same continent as the clubs they’re supporting. Ironic.