It seems like the norm of American universities is that all the letters of recommendation are always positive stuff, and they are normally evaluated on the level of specificity they have, and if they have something extraordinarily positive about the student, rather than some usual positive language. Given that they never write a negative letter, would it help my application if I ask for a letter from the professor of a class that I didn't get an A in, if the professor is a really big name in the field? (I got an A-, so not so terrible, but the grades were curved and I still got an A-.)
I was also wondering if the answer to that question would be different for applying to European universities, given that their expectations from a recommendation letter seem to be different, and they don't necessarily expect a personal description of the students' abilities.
(The professor is a really really big name. He is one of the 3 most famous people in the field in the entire world.)