Even though I so seldom post.....I must comment on Brahms, since he's my favorite....
Katchen complete recordings is not in fact complete; several pieces with no opus number are missing, for better or worse (the A major sarabande, lacking opus #, is an absolute gem -- also, nobody would guess its by Brahms). I find Katchen's recordings to be mixed. I don't generally like his tone (but that could be the quality of the recordings as well), and some pieces are played with, in my opinion, absolutely no expression at all. For example, the above-mentioned fourth ballade, which sounds like it is being expertly sight-read.
I like Radu Lupu's late Brahms recordings, and if you can find it, there's an out-of-print recording of various great pianists, plus brahms himself, playing Brahms piano music. It also includes Michelangeli playing the Paganini variations (out of order!) which is a must-have.
I agree with whoever it was that the 4th ballade is just wonderful. I wish it were more popular. I usually cannot get into his earliest piano pieces (pre-opus 10), and I really dislike the two D-major variation sets.