my two cents :
I tried by yum. it worked on one server from 7.2 to 7.3 , this server was really not customized at all, only joomla was installed on it.
It failed on another one who had some softwares installed on it : (joomla, backuppc, cacti , phpsysinfo etc.)
On that last one I remember modifying yum.conf and repositories by hand, I was not surprised not succeeding the upgrade.... So what I did was to upgrade from the CD. Worked well. i think it is really better to do with the CD and then once up again doing a "install updates"
rgds