It is hard to tell which OS is better between Linux and Solaris.
If you guys are planning to implement Exalogic, what I would recommend you is to use on Exalogic the same OS you are currently using. So if you are currently using Solaris for most of the applications you want to use in Exalogic, then use Solaris. If that's the case of Linux then use OEL instead.
Hope this helps.