Canonical (Ununtu) and Redhat (RHEL/Centos) are both rock solid distros. It's sort of a game of leap frog right now which one is 'better'.
IMHO, Ubuntu did a really good job releasing a well integrated version of their 'Long Term Support' release train with 14.04lts while Redhat kinda blew it with RHEL/Centos 7 because they didn't get some outside repositories integrated right.
For now, in general, Ubuntu 14.04 is ahead...this is likely to change in the future.