I'm happy with OCamlMakefile.
I have to say that I find it truly charming if not flattering that people are still using my ancient OCamlMakefile (which, btw., is now more than 20 years old!).
Seriously, I think that every OCaml developer should switch to OPAM + Dune at this point. The ease of developing, contributing to, packaging, releasing, and using OCaml software has improved dramatically over the years, especially with these tools. I'm generally reluctant to jump on the next build tool or package manager, but my expectation is that these tools will stay around for many years to come.