Cannot put United above Barca or Madrid, but we are definitely 3rd IMO and the only club who currently has the potential to rival the greatness of the two Spanish giants.
I'd say Arsenal and Chelsea still have a lot of untapped potential and a 10-15 year period of continued success could elevate them to bigger levels than ever before. For now, though, they're not cracking top 5.
Liverpool are the least attractive big club IMO, most players would easily choose United, Arsenal, Chelsea or City over them IMO and those are just clubs within the Premier League. It also needs to be considered that 2017-2022 was comfortably their peak period in the modern era and their appeal never really rose to the levels that it should've if they really were a top 5 biggest and greatest club ever. They also cannot compete financially with a good number of clubs, and never really signed truly big names, be that players or managers. I get that it isn't their approach but even if they tried, I don't see a 23 year old Paul Pogba going there, or a 20 year old Bellingham, or a 22 year old Haaland, or a 26 year old Di Maria, etc there are several other examples where Liverpool didn't really have a chance to get a highly-coveted superstar even if they wanted them. They need to get it absolutely right almost every time in order to be able to build a superteam, like they did with Klopp, Alisson, van Dijk and Salah.
The three big Italians are handicapped by the decline of Serie A and financial disadvantage compared to other clubs their size...the Italian teams would probably be the biggest beneficiaries of a potential Super League or something similar. Would suddenly have the two things they most desperately need: A competitive, higher level league and a much better financial situation.
Bayern are a huge club but for some reason I cannot put them in the highest tier. The Bundesliga is not popular enough and there isn't enough competition in it. No one in Africa supports Bayern. It's mostly United, Arsenal and Chelsea if I'm not mistaken. Asia and the US are similar IMO. They are a big power in football, though, and their European legacy speaks for itself...but not top 3 for me, probably somewhere between 4th and 7th.
Ajax are also a huge club but haven't really been relevant in Europe in the modern era, or at least for almost 30 years now.
PSG and City's success is artificial and comes from very unethical sources, and they have no history either. No one considers them on the level of historical giants other than kids and uninformed people. Chelsea too, btw, but it's been 21 years since Abramovich bought them and people forget with time.