My cop-out answer... Learn both
Re: ASP.NEt is propietary technology.
Nope. It's open source.
and a bunch of other projects.
Maybe you were thinking of .NET Framework 2.0, 4.x.x, which are yes... requires Visual Studio to work on.
But ASP.NET and the current Core 1.x and upcoming Core 2.x are open source and cross-platform.
--- yeah, Microsoft is very terrible in naming their products and technologies. They all sound so similar.
C# is a strongly typed language though and working in VS and it's intellisense is almost magical.
MS is embracing all things open source finally, and even making some of their products open-source and gasp! cross-platform! Can run on OSX, Linux and of course Windows. They have Angular and Bootstrap, NodeJS within Visual Studio.