I have played both the Schumann Etudes and the Chopin 3rd sonata. I would say that thay are probably around the same difficulty, in as much as they are both not at all easy. It depends what you find difficult, the Schumann covers a very large range of technical challenges and there are some extremly difficult moments, the dotted rhythms in the finale take a time. The Chopin is certainly one of, if not his hardest work, structurally the first movement is very tricky and extensive. Technically I find the Chopin very pianistic, more so than the Schumann, and for me the main technical difficulties lie in the finale of the Chopin. I would say that the Schumann is techniacally harder to learn, both are muiscally challenging and both are extremely enjoyable to play, in my experience.