Depends, personally I use both for different purposes. On a VPS which I keep without control panels and other fluff you would have issues giving access to "strangers", that is, if you sell sites, eventually you have to provide the new owner with the credentials for them to move the site, you don't want to give access to your VPS.
That's where shared and reseller accounts come in handy, as you can compartmentalize each site and provide the needed access without security worries.
In terms of performance, a VPS would likely perform better but without details about the configuration of the shared and vps accounts, there would be no guarantees.
