It's still Django obviously. You can never go wrong with Django. Mature and battle tested.

I think it will be easier to hire for Django as there are more Python devs and they can learn Django quickly if they don't know it already.

Second choice would be RoR if you want to be fancy but might be little it harder to hire for.

I'm partial to Compojure API (https://github.com/metosin/compojure-api). The thing I like about it, is at the point where I've just scaffolded a barely functional prototype, I also have a spec and interactive documentation. That documentation serves as the service's first UI. UX peeps think I am sadistic, but I like having the controls embedded in the manual.

It is also very beautiful. If you look at the examples, there are few forms (keywords, in other languages) that are not related to the domain of an HTTP API. The code is dense, but rich in relevant information.

If you want to explore the underlying architecture, look up the Ring project. It contains the lower level server primitives that several web frameworks are built on top of.

Ruby on Rails! It's a beautiful framework. It's nice to work with and batteries are included. It is well tested and battle hardened in many production environments. Give it a shot!

The ones you feel the most comfortable with.

You need to take into account new hires, development speed, community, maintainability, etc...

Laravel

Tons of PHP programmers and PHP is a lot more mature language now.

Recently used Lumen in a project. Very nice microframework based on laravel packages and a faster router.

With PHP7, I recommend reading the RFCs too. Some nice stuff on the way.

Intersystems Cache ObjectScript and Ensemble! The language is battle tested (~60 years old) and no need to worry about setting up database connections because the language has a persistence built in!

The Ensemble integration engine has adapters for almost any web protocol you can imagine and make it a breeze to create microservices.

I'm really productive with Symfony, so Symfony it is.

I'll vote for Ruby on Rails unless my app has heavy frontend requirements (Single page apps, complex ui interactions).

what's best for complex UI interactions?