I never settled with Gentoo, but something about it made me interested. Not quite sure what.
Well, it is unique. It isn't another copycat or cosmetic derivative of Ubuntu.
Actually, for the most part, it's in a league of its own.
Additionally, Gentoo is the largest distro with the source-based package manager USP. I suppose you could take issue with that approach for reasons like the systemd maintainer does where he claims it wastes CPU-cycles and time. Personally I disagree with that assessment since reproducible builds are a vital part of FOSS.
Never had a bad experience with Arch but the way they use the AUR as a crutch is a bit off-putting. It's a little bit like a giant gentoo overlay but pushes all the complexity onto the user.