I decided to procrastinate the hell out of this evening.
I spent the last 5 hours to completely rewriting the backend of my blogging-engine.
It used to be: redis
It now is: mongoDB

I saved TONS of code and have a really simple data-schema now :)
On the downside: the code is really unoptimized at the moment and basically uses a "brute force" approach to a lot of things.

Comparing the two, I have to say:
redis is simpler
MongoDB has awesome query options and is a bit better suited if I ever want to put other stuff on there (which I will!).