If I buy a single stage I would get a Forster Coax. They seem to be the cream of the crop for single stages. No shell holders as they have a special jaws that hold the case in place. Downside is that I'm not sure if those jaws fit some of the really large magnum rifle rounds, but if you don't shoot any you should be good.

I just looked it up and they can fit a rim up to 0.562" which is good for a 500 S&W Mag which is the larger than the Ultra Mags. So unless you are loading some really large rimmed Magnums you should be good.