how to choose the correct repository for new software on Centos
Notice than the most "official" solution to install recent versions of various software on Red Hat / CentOS are Software Collections.
Red Hat Software Collections version 2.3 provides both php 5.6 and 7.0, and are maintained by Red Hat, and available for CentOS users in centos-scl repository, maintained by the SCLo SIG.
An interesting solution comparison: Running newer applications on CentOS
For php just go with the remi repo. It is actively maintained and it's maintainer works for RH. You can even install it as a Software Collection.
I am one of the IUS core developers. On multiple occasions, users have given me feedback that the reason they use IUS is that it is sponsored by Rackspace and maintained by multiple Rackspace engineers. The other repos mentioned in the original question (Remi and Webtatic) are maintained by individuals. The bus factor for individual side projects is not optimal, regardless of employer.
RHSCL is the official Red Hat solution, however it has several disadvantages as compared to to IUS.
- less frequent updates
- usually a shorter life cycle
- arguably more confusing usage