We are trying to determine the best approach for adding a complex API layer to a modified version of nopCommerce. To back up a step, we're building out a custom site for a fashion/apparel manufacturer that has a lot of front-end application requirements and also needs to integrate with their cross platform apps (iOS, Android, Windows) which we're building with Xamarin. We've tentatively decided to start with nopCommerce as the base of our application to which we will add an API layer.
What we are unsure about is what is the best approach for implementing this in nopCommerce (or other similar .NET package)? The options we are considering are MVC vs WebAPI vs ServiceStack. We've been going thru many of the tutorials on PluralSight.com to get up to speed on app dev and API creation best practices, but there seem to be so many options, we're not sure where to start. We seem to be somewhat lost in a sea of implementation options for the API and how each is to be evaluated based on choice of the JS packages/frameworks used on the front-end for the web site and the tools chosen to create the apps.
If it matters, our basic requirements are:
Expand core of basic e-commerce package with some custom ERP style functionality
API layer that can work effectively with both a web front end (possibly as a SPA) and all cross platform apps built using Xamarin
Insure OAuth authentication across all interface types so we can just use social media logins consistently everywhere and can authenticate the user in any environment
Given this...
My question boils down to which of the three API methods (MVC vs WebAPI vs ServiceStack) is best for this?