I highly recommend that anyone interested in Brahms put sonics aside and go
here to obtain Toscanini's incredible 1940 performance of the Symphony No. 1. This performance, IMO, towers over many others I have heard, and the work, IMO, is one of the supreme masterpieces of the symphonic literature.
I recently listened to this on my main system, and found the 1940 mono recording to be surprisingly listenable, and to not detract significantly from the performance, which I can only describe as magical.
Among early mono recordings, I also recommend Kathleen Ferrier's 1947 performance of the Alto Rhapsody, which I have on a Decca LP.
For good sonics + good performance, Uru975's mention of Hyperion prompts me to say that that is an excellent label generally, and you may want to peruse their catalog of Brahms recordings
here. Also, you are unlikely to go wrong with any of the recordings of his chamber works that have been issued on the Harmonia Mundi France label, or, for that matter, with pretty much anything else on that label.
Regards,
-- Al