Theres a video on this topic.
https://www.youtube.com/watch?v=y62-ce8TBko
The conclusion from this guy was that both of the cases offer great quality and are suitable for any build. However, he states that the lack of an optical bay in the H440 to lose the competition against the R5. On the other hand, the R5 doesn't offer different colours for the case unlike the H440 and only comes with 2 fans included.
Here are the pros and cons for the 2 cases.
Fractal Design Define R5
+ Simple design & variety of colours
+ 2 optical bay slot
+ Simple assembly process
+ Outstanding cable management
- Only 2 fans included
+ Excellent cooling & really silent frame
NZXT H440
+ Elegant looks & variety of colours
- Lack of an optical bay slot
+ Simple assembly process
+ Chamber separation
+ 4 fans included
+ Sufficient cooling for enthusiast systems
Personally, I would go for the R5 due to the case being better for a cooling system and the sleek matte black design.
However, if you are looking for a case with more features for the design, go for the H440.
There is also a Razer H440 version so if you're a Razer fan, go for it.