Don't do it cheap at 99designs. That's the equivalent of writing your site in ASP.net: it looks like a good idea now, but soon, you'll regret it.
ASP.NET Webforms? Yes, huge mistake you'll regret
ASP.NET MVC? Fantastic choice, you will not regret it so long as you're a microsoft based shop
You can't make a blanket statement like that about ASP.NET, since it's effectively a bifurcated ecosystem at this point (and we're all hoping the WebForms fork dies a quick death).