to be fair to LibreELEC i would not really suggest or imply that one is really better then the other as CoreELEC is basically pulled from LibreELEC and CoreELEC will merge with LibreELEC' master which they actually just did not all that long ago.
I monitor and build both systems probably every other week or so by building the Amlogic S912 and some S905x projects on a couple of different Linux boxes ranging from 15:04 up to 18:04 as i refuse to use docker or any virtual setup ( im to old and old school, lol) i do it just to see where they both are and think in most cases the differences people sometimes see is more based on what box they are using and where the development for that box or derivative sits in each of the respective systems.
RIght now at this time i would say CoreELEC is working pretty good on the boxes that i test it against and the rom/game support is working great as well, while if i was on a Rockchip or O-droid platform its easy to see from their respective github time stamps that LibreELEC is has been more active the last time i looked.
LibreELEC was started and built off the older OpenELEC to better support other boxes and forks like CoreELEC took LibreELEC and did ithe same thing as the developer was trying to support what he wanted to do and theres others that do the same thing. Its hard and extremely time consuming to try and create a build system that can work on SoC's from different manufacturers and being pretty much all the coding is being done by people giving up their free time to help others creates different forks.
"better" or "worse" are terms i try and encourage people to understand the reasons why one may be considered ahead or behind when it comes to the differences when making comparisons. Coders in some cases can take things really personal as its their time and output that the public benfits from and its easy to in some cases upset people which ends up driving people away or going private and not publishing public stuff and this sport is no different then any other and happens all the time. Kodi is a perfect example of that and anyone that has followed the xmbc/kodi scene since the beginning is aware of what i am talking about.
To be fair...LibreELEC it is by far the most overall active and the people involved are a huge part of driving this part of the sport and depending on which coders are active at any given time tends to be a bit up and down based on the wide amount of SoC's its trying to support.
As suggested its best to actually test for yourself and see what works best for yourself at any given time as things change all the time.