A modern programming language that makes developers happier.

kotlinlang

I run Spark services, ktor services and Dropwizard services in production currently, I've also played around with Vertx. 
A very brief evaluation is, Dropwizard, Vertx and Spring boot, I all consider quite heavy both in what you need to learn around the framework and in them amount of "stuff" they bring with them. That being said our largest most used app runs dropwizard and has been very successful over the years. Recently however we've made a shift to lighter smaller services, and those much prefer the lighter weight of Spark/KTOR.