I think that the 1st mvt. of the Waldstein is terribly underestimated in terms of difficulty (I find it MUCH harder to play than the third movement) and the main reason for it is that IT IS TERRIBLY UNPIANISTIC (esp the developement). Lots of broken chords requiring quite unusual hand positions. The third movement gives you lots of moments of 'relief' , but the first is 10 minutes of 100% concentration ..the slightest of lapses can cause big slips ...it is intercrossed with runs and broken chords and trills.
I would be interested in knowing the comments of someone who has played both of them. Personally I would compare both the sonatas this way: The 3rd movement of the appasionata is slightly more difficult than the 1st mvt of the Waldstein, and the 3rd mvt. of the Waldstein is more difficult than the 1st mvt. of the Appasionata...2nd movements cancel out ( since there isn't much, technically, in either of them).