You have to consider not only the language but what the team working on it will look like. It is still a bit hard to find server-side kotlin devs. On the other hand in my experience, Java devs pick up Kotlin really quickly (as do Python devs interestingly whereas they struggled with Java).
I'm a huge proponent of Kotlin on the server side, less on frontend (JS) side.
If you go with Kotlin and Spring Boot, Micronaut or even just Ktor,you'll likely not regret the choice. (I have no experience with DropWizard).
Now if you choose Java it will not be a horrible choice either, and it is not too hard to convert to Kotlin later if you need/want to. I've heard cases of people going back to Java a few years back, mostly for compiler performance reasons, but there has been a lot of effort on that recently. And while compiling Kotlin is still slower than compiling Java, the fact that you can divide things more easily in multiple files and incremental compilation compensates in most cases (except of course in the case f a clean build).