Connecting the Cisco IOS Voice Gateway to CUCM via SIP has been the preferred way to do it in the past couple of years.
The slowly dying H323 protocol (ISDN based) is not being developed anymore while SIP (HTTP based) became the industry standard for VoIP. So whenever PSTN connection is implemented via an IOS Voice Gateway, the choice should be really between SIP & MGCP.
Prime Collaboration Assurance deployments (PCA) became very popular since Cisco has started giving it away for free (standard version) with new orders. It is indeed a great tool for those who are willing to make the effort and make it so. Are you?