"Ah, but is the Pergamon better than a Museum of Natural History (country and continent unimportant)?"

It is for me personally as I have always been fascinated with ancient history.

Very interesting and insightful replis from all of you. Now I learnt about another museum in Russia, which I will try to go one day.

On the subject of "opinions" I agree Aramis's points and Thin,I understand what you are trying to say but I wish to tell you this. Everything can be compared, as long as the criteria and objectives are clear. In my case, as a tourist, I can even ask, "How is Eiffel compared to Louvre ? Which shall I visit if I can visit only 1 for 1 hour in a afternoon ?". So why can't different types of museums cannnot be compared ? Even anyone who knows nothing about art can still enjoy visiting one.
BTW, choosing a museum to visit is NOT confined to their collections. I will visit the Pompidou Centre even if I have no time to enter it. Still, thanks for your replies.
Now, sorry for those French examples although this is Berlin.

Danke and please carry on.