I used to use two tumblers, one with walnut for cleaning and one with corncob for polishing. Midway brass polish in the corncob did improve that step. Some guys add Nu Finish or carnauba wax to media to enhance performance.
I don't recall what walnut media I used because I filled my old Midway 2092 with it back in the early 90s (it lasted 20 years), but it was ground finely enough that it did not clog primer pockets and flash holes. You might find yourself picking media out of cases and it gets real old very quickly. I also used corncob media that was actually blasting media, and that type also did not pack up and create extra work, and it did an excellent job.
When my 2092 bit the dust I shopped around and decided to go with a rotary tumbler and stainless media. I don't care for the extra trouble of having to deal with the water and having to dry the brass, but the results just cannot be beat.