Is Best Possible

I read an interesting post  in Listen which made me thing about the word BEST, in connection to art or a body of work by a specific artist or composer, and whether it is at all possible to determine what an artist best piece of work is.
Who would determine that - the artist himself? Fellow Artists or composers, critics? Or in the case of composers - performers?
Would this Best Piece be perpetually the best piece, or would it change according to different criteria?
Personally, I have a hard time with the concept, especially for composers - because the interpretation has a lot of weight in how the piece comes across.