Jane Street Core has to all intents and purposes solved the standard library problem. I admit I had my doubts in the past which one of Batteries or Core would be the "winner" so avoided them both and stuck with the default standard lib, but I think anyone starting a project today should start it on Core.
This may get better with the latest OCaml, but Core-powered binaries are ginormous. And AFAIK, Core doesn't work with js_of_ocaml (and I'm not sure if it works on Windows at all).
