If software performance is your top priority, then Scala/Play is probably best. If developer productivity is your top priority, then Ruby on Rails is the best choice in my opinion.
The Rails framework is batteries-included. The framework takes care of many things by default so that you don't have to. Logging, security, etc. It's also well-integrated; for example, controllers understand models out of the box. I had a better experience with RoR than with Play.
On the other hand, Scala and the JVM are more performant in general, so they can scale to serve more requests per second on the same hardware.
If you're considering serverless functions, then Scala is probably a better choice because it would be faster to load, giving you better economics.