I've been using IUS in the past. They have a good way of naming their rpms, so they don't interfere with the RH rpms. But they don't support older CentOS versions still on extended support as long as I needed them. And they don't provide as much php-related rpms (f.i. pecl-stuff) as remi does. So, with newer PHP versions I had to go to remi's repo. Combined with EPEL (and rpmforge being dead, anyway) it's working quite fine here for PHP 5.5 and 5.6. He provides files for CentOS 5, 6 and 7. The only caveat is that he uses the same rpm names as with the original ones. So, you have to give this repo the same priority as the base repo has. In consequence you have to be careful what it wants to install as dependencies and exclude a package sometimes. But all in all it works very well. I've used the webtatic repo once for a special case. I don't know exactly why but I wouldn't recommend it. If IUS provides the version you need I'd go with that. Kai