the two rachmaninoff's are difficult in different ways. The rhapsody is primarily a counting issue, but the soloist is less reliant on them, so it doesn't matter as much if they mess us. The second concerto isn't incredibly technically difficult like I've said, but they play a much larger role in the big picture, so if I was choosing between the two and I was playing with a questionable orchestra I would go with the rhapsody ... Not that I'd choose a piece based on the orchestra I was going to be playing with. Its just annoying to listen to the rach 2 performed by amateur orchestras that can't play in tune, because you hear them all the time! Again, rhapsody and 2nd concerto, different difficulties, depends if you want to challenge the orchestra in counting, or just intonation and big picture. Of course these are concerns in ALL of hte pieces, but I think predominantly in teh works by rachmaninoff. hope this helps some.