Oracle 18c RU (Release Updates) versus RUR (Release Update Revisions)
Generally my understanding is RUs will contain the most current bug fixes and security updates.
RURs lag behind RUs in regression bug fixes (at least one quarter – I’m verifying the exact lag time), but do contain current security fixes – applying RURs could be considered a more conservative approach, unless you are suffering from a bug fix that is in the current RU and you really need it.
Just my opinion, apply RUs quarterly or as frequently as possible as you will get the bug fixes too. New optimization techniques will not be turned on by default in RUs so you don’t worry about radical performance differences.
Thank you to TGA – for pointing out a mistake in this blog that I have hopefully corrected.