What is best for auth ASP.NET MVC REST API? OAuth 2.0 or OAuth 1.0?

We are building a REST API using ASP.NET MVC. This API is similar in principle and usage to the Factual v3 API. They use 2-legged Oauth 1 for their API. Our design is very similar in that applications, primarily mobile will use our API behind the scenes to provide a service. The end user of the application will not know about our API, and will therefore not have any credentials. So redirecting the user via a browser window to an auth form (like facebook) does not make any sense. My questions are..We are building a REST API using ASP.NET MVC. T