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Spring (normal or boot) MVC, mostly.

Or Jax-RS/Jax-WS with Jersey/CXF/whatever, if you want to stick to standard EE technologies.

95% of our stuff is Java/Spring (big SOA, banking sector). ESB/Gateway is normally Mule or Camel.

do you have experience with other stacks (e.g. Play, Node, Ruby)? What's your experience with them?

We used Python with Django (and django-rest-framework) in my old (non-financial) shop, and it was fine.