http://I use a Lyman 2500 pro vibratory tumbler and find it fantastic. The bigger the unit the bigger the stuff you can put in it. I use corn cob as a medium but a lot of people use walnut shell.
I've got this one too and have been happy with it so far. I was thinking like you, get the biggest one I could so I could fit in the biggest parts possible.
That said I would still like a polishing wheel to compliment it.
