Choose between Web API and WCF

=> You can choose the Web API when you want to create the service that uses all the HTTP features, such as request and response header, URIs, versioning etcetera.
=> You choose the Web API if you want to expose the HTTP services to a broad range of clients. These includes the mobile , iPhone and browsers.
=> HTTP only. First-class programming model for HTTP. More suitable for access from various browsers, mobile devices etc enabling wide reach.
=> no support for higher level protocols such as Reliable Messaging or Transactions
=> Web API is the great framework for exposing your data and service to different-different devices. Moreover Web API is open source an ideal platform for building REST-ful services over the .NET Framework