I think it depends on what you are trying to achieve. They are all slightly incompatible to some degree. I've written quire a few libs in .Net Standard and had

I think it depends on what you are trying to achieve. They are all slightly incompatible to some degree. I've written quire a few libs in .Net Standard and had them work on all three platforms, as well as writing Core command line apps and ported them to .Net 4.5. The issue is more with stuff like ASP.Net Core etc, where the libraries are slightly different conceptually.