Yes, you have to pick up front what you want. The nice thing, is MVC4 will automatically use HTML5. It won't automatically be responsive, but it has things built-in to handle different devices, provided you do some of the work. http://www.asp.net/mvc/tutorials/mvc-4/aspnet-mvc-4-mobile-features.

I don't know how standard ASP.Net handles HTML 5/mobile, but Microsoft is moving to "one asp.net" that supports mobile, html5, etc. How you use those features is your choice of ASP.Net, MVC, etc.

>First, thank you for your message. Just to clarify, I do not want to mix and match. I will decide on either web forms or MVC and - hopefully - will stick with just one technology. But first I want to create a project in VS 2012 and create a main page of the application. I would like to use HTML5 for the main page utilizing responsive design. But now - as I type this - I realize that when creating a project in VS 2012 I have to select either ASP.NET MVC or Web Forms. So it look like before I even create a main page UI I have to make the decision on Web Forms or MVC. Is this correct?