A standard vSwitch (vSS) is configured on every host manually or scripted. A vDS is created at the datacenter level in vcenter and configured once and hosts added to it. Portgroups on vSS are also similarly created manually on each and every host, vs vDS at the switch level, and automatically available on all hosts.
A vSS network stats information is local to the host only, but a vDS stats are maintained throughout at vCenter level and follow the vm from host to host.
vDS is dependent on vCenter, vSS is not. For this reason, I use vDS for vm networking, and use vSS for management portgroups.
-KjB