[dtien]

I'd go Django first to understand the basic terminology, concepts, and patterns that are used on the backend. Django is old, but feature rich as the parent said, yet still heavy development and use. So the ideas and concepts you'll get from it will still be very valid.

Than as you get comfortable you can branch out into the less meaty frameworks like Flask or Go ( if you want to call that a framework ).

Remember, beyond the actual application server and framework, there's all the other 'stuff' that goes around it. The web server, databases, caching technologies, etc. Take the well travelled path first to see the best practices, than go your own way if you really do want to 'wire stuff' yourself. ( And trust me, even with Django there's plenty of wiring required still to build a real app ).