Java vs C# ASP .NET MVC?

Question

Java

Greetings, I am facing such a dilemma, I cannot choose a programming language for a Web application.
I used to code in C#, I really liked the language, and over time I began to look towards the Web.
Before me is such a task, to make a website with a very large audience. So, with the help of which it is easier and more expedient to make a website, and also in the future to write an application for mobile OCs on it (ala Facebook, VK)
As I understand it, cross-platform Java affects here, but is it really impossible to write an application for other operating systems (Android, iOS) in C#, or will speed suffer?

Answer 1

but is it really impossible to write an application in C# for other operating systems (Android, iOS), or will the speed suffer?

It is possible xamarin.com
will not be slower than java.

Answer 2

I think it will be easiest to make a site on ASP.NET MVC (actually, the site itself) + WebAPI (API for a mobile application) + SignalR (high loads) + PhoneGap (cross-platform mobile applications). All in one, convenient.