ASP.NET Ajax vs ASP.NET MVC

Hi,
Till now, all web development I'm using ASP.NET Ajax. I never change my development style into ASP.NET MVC. If I maintain using ASP.NET Ajax and don't want to using ASP.NET MVC, what's the benefit will gone? What ASP.NET Ajax can do, and what ASP.NET MVC cannot do?
What ASP.NET MVC can do, and what ASP.NET Ajax cannot do?
What the most significant benefit to use ASP.NET MVC?
Need advice