ohh.... btw, the way i ranked the pieces is based purely on the technical difficulty while i learned them... it's my belief that musicality is an add-on after you've learned "the notes
i agree with Skeptopotamus that the sonata no. 2 is musically difficult. however, the good thing is, too many people perform them, pretty much anybody in any competition (well, figuratively speaking) plays the piece, so there's a really well-defined guideline we can follow (suppose you find the easy way out by combining how other people interpret the music and come up with your own)...
however, sonata no. 1, if you study into the music, you'll find too many magical things embedded in the technically difficult passages. at the intended tempo, it's rather difficult to bring them out musically...
about the difficulty of concerto no. 3, (imagine you haven't learned the piece), when you look at the music, you can follow it through, the notes are there, somewhat difficult (i found that the notes for the 2nd movement is rather a bit more intimidating while you learn), but you know if you can manage it at slow speed, with enough practice, you know you can graduate increase your speed with all the correct notes, musicality aside.... but with sonata no. 1 (throughout all 3 movements, many of you must remember when you worked on ravel's scarbo, it's like that, it's very difficult to even follow the music through... for me i find that scarbo is the most difficult out of these rachmaninoff selections....
musicality... while, russian music is full of very musical moments, but you must agree they are not exact abstract... not like some contemporary american compositions like rzewski where you may need to study the piece with him to know what's going on...