There's not a lot of difference between any of the major tumbler brands. I'd buy one based on capacity and price. The media separators do a lot of the work, but you still need to make sure each individual case is clear.... not much more trouble than doing them all manually without the separator.
Media.... I use corn cob, 'cause it's cheap. Seems to last just as long and get the cases just as clean as walnut shell media. I also add a dribble of case polish.... but NOT Brasso.
I'll pretty much echo wwb on this as it is what I do/did for my tumblers. I have both a vibratory and tumbling "tumblers" as the second has a special purpose that the other can't fulfill. The vibratory case cleaners will do 98% of all chores if not more. I bought mine back before a "media separator" was included in the package so I use a plastic colander for that purpose. I place the colander in a 5 gal pail that I have a couple of rods through to hold it in place with the top of the colander even with the top of the container. I snap on the cover and shake vigorously. A minute or so of this gets out the vast majority of media and I have little dumping of excess media to do. If I were in better shape I might be able to shake it all out but a minute or so is the best I care to do.
I do agree that capacity and price are major influences in one's decision but also look at the physical space the machine takes up. My first vibratory cleaner was rather wide for its capacity and took a lot of bench space. I eventually replaced it with a slightly smaller machine that fit on an upper shelf I did not use. I personally would rather clean cases more often than hit my elbow on a tool.