well i believe the main thing it depends on your infrastructure, hardware you have, and the design needs
each apreoach has its advantages
for example technically
if you are using TMS for meeting booking both VCS and CUCM registration will work
however the phonebook currently work differently if you register it to VCS then TMS will push the phone book while registering it to CUCM it will use the directory from CUCM
SIP dialing and dial plan design will be differnt based on where you register the end point but only design and call routing differences
if you are using CTS end points registered to CUCM with the new versions you can have direct calls with out the need to interop using VCS or CUCM registration
Hope this help
