Over the years I have tried both corn cob media and walnut shell media. The walnut shell media is aggressive and leaves the brass with a dull shine. The sizing die usually burnishes the cases to a brighter smoother shine. The corn cob media, which I no longer use, is a better polishing agent but can leave stains on the brass because it is not aggressive enough. You can get walnut shell media from gun stores, or even from Harbor Freight (sometimes?). It seems to last forever if you refrain from putting polish in it. Shinny brass shoots no better than the brass that comes directly out of walnut shell media without polish. I am into shooting, not making ammo look like pieces of art.
The carbon coating left inside is no detriment to the accuracy of the ammo. It aids in seating the bullet by acting as a dry lubricate as the bullet is seated into the case. I make no attempt to remove it. I do shake out any cleaning media as I remove the cases from the tumbler (actually I use a Dillon Vibratory Case Cleaner often misnamed a "tumbler" and their Case Media Separator unit).
I tried the spray lubes and they are too messy and often get too much or too little lube on the cases. I roll my cases (rifle only as all my pistol dies for straight walled cases are carbide and do not need any lube at all) on an RCBS pad using their case lube from a squeeze bottle:
If a particular lot of brass seems reluctant to allow bullets to enter the throat of the case then I use the NECO CARTRIDGE CASE NECK DRY LUBRICATION KIT which is a small tin of Moly dry lube with small ball bearings in it that act to pass the Moly onto the inside of the case throat when the throat is plunged into the tin:
When the cartridges are reloaded I first wipe them off with a damp rag then roll them on a towel to dry them. (The RCBS lube is water soluble.) During this process I look for reloading defects like upside down primers and any splits I may have missed earlier.
This all works for me and you, of course, can choose to do your ammo any way you like. I like my way!