Hi
Good advice from
BeerCan but I'd advise taking the time to use Ubuntu, I'm a CentOS -> Ubuntu convert. Pro's of Ubuntu over RHEL based distros.
1. They have an LTS version, currently 14.04, supported for 5 years, this is the version to use for Telecoms systems. RHEL based distros also have long support times.
2. Regular release schedule - LTS version released every even year in April, e.g. the next one will be 2016/04. Release schedule for RHEL distros depends on the upstream provider, Redhat, so who knows when the next is to be released, making it difficult to plan.
3. Upgradeability, you can upgrade from one LTS version to the next without reformatting your hard drive. Again an advantage for Telecoms systems. Not possible with RHEL.
4. Larger repository than with RHEL.
5. Usually packages such as PHP are more up to date than they are with RHEL.
6. Popular system, so lots of help and resources on the internet, especially for those whose Linux skills may be termed "Conversational"
In terms of performance, there is probably nothing between them, nor is there anything between them in usability, other than the afore mentioned repository.
Joe