Wow! You are getting a lot of helpful replies!

Most of Brahms solo pieces for piano are advanced (beyond grade 8 ) and intended for mature pianists with an accomplished technique and advanced musicianship. As such it is really not possible to “order” most of the pieces you mentioned in progressive order of difficulty. They are all equally difficult – although the difficulty may be different in specific aspects. Also bear in mind that difficulty is personal: what may be difficult for me may be easy for you and vice – versa.
The easiest pieces are his Waltzes op. 39 – especially in the four-hand version. Later Brahms rewrote them for 2 hands, and there are two different sets: an easier one (which ranges form grade 5 – grade 8 ) and a more difficult one. The easiest are op. 39 no. 2, no. 3, no. 9 and no. 15
Next come the Hungarian dances, again in 4 hand form. Once more, Brahms rewrote them for two hands, but they are far more difficult than the Waltzes. In fact, Brahms achieved here the dubious honour of composing pieces that are far more difficult to play than they sound.
Next level would be the Intermezzo in E major op. 116 no. 6, the Intermezzo in Bb op. 76 no. 4 and the Intermezzo in A minor op. 76 no. 7 - around grade 7 (if you want some obscure pieces at this level, try his “Two Sarabandes” in Am and Bm – the first one in Am is possibly the easiest piece that Brahms wrote).
Next the Ballade in Dm op. 10 no. 1; the Intermezzo in A Op. 76 no. 6, the Intermezzo in Am op. 116 no. 2,the Intermezzo in Em op. 116 no. 5, the Capriccio in Dm op. 116 no. 7, the Intermezzo in Eb op. 117 no. 1 (the easiest of the op. 117), the Intermezzo in Bbm op. 117 no.2, the Intermezzo in Am op. 118 no. 1, the Intermezzo in A op. 118 no. 2, the Intermezzo in C op. 119 no. 3, the Rhapsody in Gm op. 79 no.2, and the Romanze in F Op. 118 no. 5 – all around grade 8 or slightly above.
Everything else is advanced.
Best wishes,
Bernhard.