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.
It’ll be interesting to see if people will remove Ajax from this list in 20 years. A great history and the melting pot for most great Dutch players. Now, they’re a smaller European giant that is unlikely to have any impact on the CL and who probably won’t hold on to any Dutch starlets past their 18th birthday.