In case anyone is interested in a comparison between APIMatic, Swagger Codegen and AutoRest (another free, open-source code generator), I did a little comparison here: https://disq.us/p/186qs52 (May 2016)
There's also a discussion in HackerNews: https://news.ycombinator.com/item?id=12485310 (Sep 2016)
Hope this helps you make the right choice.