Verified answer

I will assume that you are asking about the technical elements of the concertos.

In which case, I don't think either movement is considerably more difficult than the other. They are both filled with octave passages and some fast-paced running scales. But I would say that overall, Tchaikovsky's 1st is a little more difficult. The balance and control of sound working with orchestra is pretty challenging stuff, and you deal with a greater range of sound all the way from playing under the orchestra to dominating the concert hall with those fat chords.

But really, it depends on the pianist. I'm sure there's a mix of pianists who have different opinions on which movement is the more difficult. :)