What is the difference between RSTP & PVST+

RSTP(Rapid Spanning Tree Protocol-802.1w Standard): it is the enhanced protocol of STP,
the main caracteristic of this one is Faster than STP (it converge in less than 6 seconds).

PVST+ (Per Vlan Spanning Tree Plus) : This feature is used to create an instace of
STP for each VLAN. e.g.

If you have a switch with 3 vlans you will have a 3 instances of VLANs that you could
modify the parameters (like to make root bridge for a specific VLAN) independently
according to your design goals.