I've loved a lot of Idol covers that have come out. Kanata's is beautiful, and nene's has this absolutely contagious genki energy she always has. Irys' is technically perfect and I really liked the instrumentals on Koyori's, plus she sang it really well. I also enjoyed Kotoka's outside of Cover.
Mori's is my favorite, but if someone had a different opinion I would understand, music is a very personal thing, there are hardly many objective truths in such things since different people value different things. For me, Mori put a musicality in the slower lower verses and a power in the build ups that made me love it even more than the others.
https://youtu.be/JmZRrKEqG2M