I have gone through many articles to understand why we need WebApi's when we can create restful architecture using WCF rest services but could not find some solid reason. Can we use these interchangeably? Are these just two approaches to solve similar type of problems. Or else there are some things/features which each of these can do but other can't. Please help me to understand, how I can decide which one to use based on given scenario.
Although WCF provides some support for writing REST-style services, the support for REST in ASP.NET Web API is more complete and all future REST feature improvements will be made in ASP.NET Web API
So for REST services it's preferable to use Web API, not WCF
That link also provides some useful info (like whether they are interchangeable, features of technologies)