The way I've viewed it is WebForms is what you learn when you're starting out, and when you want more advanced features that are built for websites people actually use, you use something more sane, like MVC.
In my experience, "vanilla" Asp.NET (with WebForms) makes a ton of assumptions on how it should be styled, based on...I'm not really sure. The Visual Studio project team's intranet or something. MVC is slightly better with CSS adapters and the like, and provides a more robust routing mechanism that we've used on a few sites.
Why is this a debate, other than being more platform religion?