I think it soley depends on your ability and interest on those domains. They are completely different fields of IT. I do somewhat similar to DeVOps per say . I would think that DevOps is a fancy name for system admin for products usually in cloud or in virtual environments. If you have general IT experience and good understanding of software workflow, DevOps should be fairly easy to pick up. DevOps can be fascinating and incredibly challenging at the same time ...so many tools and technology to learn from.

Hadoop on the other hand I hear is complex right from the start. The things it can do is complex is used in conjunction with other complex products and to be good at hadoop you have to be good at programming ...really good. That's my thought after installing and playing with hadopp / yarn etcs.
That being said I have seen people just push jobs on hadoop for a living and make 6 figures so LUCK I guess is also an important factor.
Hadoop is fairly new and in my opinion will be replaced with some new stuff soon like for eg spark or bigquery. Mapreduce is just the tip of the iceberg...
I think of Hadoop as an ecosystem more than a technology...database / cluster / spark / storm / pig ...etc all falls under that ecosystem.


Good luck