I've worked on generating SDK's for a small startup last summer. I haven't tried AutoRest but I dabbled with ApiMatic and Swagger and ultimately went with Swagg

I've worked on generating SDK's for a small startup last summer. I haven't tried AutoRest but I dabbled with ApiMatic and Swagger and ultimately went with Swagger. The biggest thing for me was that, while ApiMatic has a lot of really nice tools and options, I couldn't find any way to customize the actual generated code. With Swagger, all of the templates are community made and freely available, and it uses mustache templates, so it makes it really easy to customize. This was important for my company because we had some custom options we wanted the SDK to handle that weren't necessarily reflected in the API, and convenient helper functions for authentication. I think the community part is definitely a huge plus for Swagger.