Rails - because Ruby is easy to learn, especially for beginners and you get great, custom things done in no time. Also Rails forces you in some patterns that make sense in my opinion. Testing is also fun.
I don't agree: from my experience (~9years of full time Ruby/Rails, including teaching and coaching) Ruby is not easy to learn, at least if you want to know what you're really doing. And Rails, as is, promotes several anti-patterns that will mess your app after 6+ months. Fat models are a bad practice, models as form objects are a bad practice, developing uour business logic almost totally on top of models is wrong. That's why some experienced Ruby devs are moving away from those anti-patterns by promoting real object oriented approaches: for some good examples check hanami web framework, rom-rb and Trailblazer.
My 2cents reply.