They are both great platforms and I use both, including WPF. Silverlight, however, may not be receiving a great deal of community/Microsoft support in the future. So you need to factor this in to your decision making process. MVC, on the other hand, has a great deal of support from both the dev community and Microsoft. Plus, it's been my experience that it's easier to find MVC talent than Silverlight.
Since you have no or little web experience, the learning curve may be a little tough for MVC. If your desktop experience is winforms, then transtioning to Silverlight will also be tough due to the XAML learning curve. Also, the Silverlight route may aid in the transition to Metro XAML/C# stack, if that's important to you.
If I was in your shoes and I had to make a decision between the two, I'd opt for MVC.