何时使用ASP.NET MVC与ASP.NET Web窗体？

One of the common questions asked regarding ASP.NET MVC is why should you use it over ASP.NET Web Forms? The answer generally includes ViewState and clean URLs, amongst others. Towards the end you'll find a blurb about using the right tool for the job and that they serve different purposes. However, I don't believe I've ever seen what those purposes are. So, when would you actually choose ASP.NET MVC over ASP.NET Web Forms, or ASP.NET Web Forms over ASP.NET MVC?One of the common questions asked regarding ASP