I tried various different ROMs in different versions of Android, and this one is by far the best:
Android 9, still actively receiving security patches from the maintainer. Far less buggy than the final release from ZTE themselves. I'm fact, it's been dead reliable since I settled on it a couple weeks ago. Excellent battery life, too.
I was honestly looking to get rid of my Axon 7 when I started this search, as I was particularly sick of some of the irritating bugs the phone had (mic stopping in speakerphone???).
All are gone. I wish I could have had this experience in the software side for the last 2.5 years I've owned this thing. I love this phone now.
Definitely use the universal boot stack of you want to save yourself some headaches.