MVC4 Web API或MVC3 JsonResult

I've seen a lot of arguments for why moving from WCF to Web API is a good move, but I haven't seen much on migrating from a controller with JsonResult actions to a Web API project. Can anyone provide the main benefits on switching to the Web API platform, or does it make sense to not migrate and stay on MVC3?I've seen a lot of arguments for why moving fro