it seems like Camomile is more widely used in the community.
I have no particular recommendations as I have not used Camomile, but this isn’t my experience.
Going purely from the imperfect metric of opam rev-deps:
ᐅ opam list --short --depends-on uutf | wc -l
31
ᐅ opam list --short --depends-on camomile | wc -l
18