What are the use cases where one is preferred over other ?
PTP is an IEEE Standard which means it is simply a published document establishing specifications. It is up to vendors to implement the standard.
Per Wikipedia's List of PTP implementations
Precision Time Protocol (PTP) is a widely adopted protocol for delivery of precise time over a computer network. A complete PTP system includes PTP functionality in network equipment and hosts. PTP may be implemented in hardware, software or a combination of both.
Wikipedia's Precision Time Protocol page states:
IEEE 802.1AS is an adaptation of PTP for use with Audio Video Bridging and Time-Sensitive Networking.