I just released a major public site on the MVC platform after using webforms for all previous projects. Without a doubt it is the way to go, IMO.
With webforms, I have found the sites tend to become a mess over time as you have blocks of code in the code-behind that handles both view logic and controller logic. As the site grows and the logic gets more complex it is difficult to trace what is happening and where.
I find that that MVC forces you to break things up in a more logical manner. Controller and model classes allow you to get a better control on the organization of the application. In addition, views are more flexible because there is a specific way of providing data to them, through models.
Also, like others have mentioned, you have more control over the markup and urls and it plays nicer with client libraries like mvc.
The only time I would use MVC is if I was building and intranet site that was focused on reporting data of some sort where the built in controls that come with asp.net would save development time and I wasn't as concerned with the look and feel. I would never use asp.net webforms again for a major public facing site.
