Prokofiev's 3rd is great, but it isn't the best, in my opinion. I could make a very long list of various Russians' accomplishments, for they have excelled at writing piano concertos. Rubinstein did write some good piano concertos, and I would say that the 3rd and 4th are the best of them. I wouldn't put Rachmaninoff's concertos in that list, simply because I think they are more Hollywood and virtuosity than substance, even though they are nice to listen to. However, I would put Tchaikovsky's 2nd up there also. Going in another direction, I would also put Schnittke's Piano Concerto from 1960 and his Concerto for Piano and Strings up there, for both pieces are quite moving pieces, the first one being quite similar to Shostakovich or Prokofiev and the second one a very dark work.