Well, it depends. Emulations tend to have more problems, but also genuine Adobe Postscript may have problems with some documents. For most stuff, an emulation will just be as good as the original version. For some more advanced things (e. g. for proofing), you may not have all options available.
Are you thinking about buying one specific printer? Or are you looking for a printer in the price range xxxx-yyyy $/?, color or black and white, etc.?