The story isn't as dire as it sounds like. Yes there are multiple stdlib alternatives, but I wouldn't classify any of them as a "wrong" choice. They interoperate pretty well, and using one stdlib alternative will not block you from consuming libraries where the maintainer chooses another stdlib alternative.

I tend to look at this situation as there are multiple really high quality options to pick from. Base [1], and core [2] and containers [3] are the three options I typically recommend people to look into (if they are interested in options outside of the stdlib), and all three are really high quality. Your decision could end up being as easy as deciding which platforms are important for you, if you don't care about windows and need to work with unix apis then core or containers are excellent options. If you do care about windows, then starting with Base/Containers is an excellent choice.

[1] https://opensource.janestreet.com/base/

[2] https://opensource.janestreet.com/core/

[3] https://c-cube.github.io/ocaml-containers/

Some additional notes:

* Core can be seen as an extension to base as it has a very similar API (It re-exports many modules from base), and it adds some unix related utilities and additional data structures.

* The built in Stdlib in OCaml has also been improving and if you are able to use a recent compiler version you might not feel the need for an stdlib alternative.

* Containers is an excellent "default" option as it tries to provide a similar API as the stdlib and works on all major platforms supported by OCaml.