A lot has already been mentioned...
No existing niche is really 'easy' today.
I see quite some suggestions for broad niches, ignore those suggestions!
Long-tail keywords point to areas with less competition and that is where you want to focus to be! So keyword research is an area one wants to be comfortable....
When writing articles, go for sub-subniches, do son't write about 'Pets', 'Dogs', 'Small dogs' but about 'the best food for my Cocker Spaniel'. Again longtail keyword research should help you finding your topics...
If you will write your content yourself, the 'easiest' niches are the ones you are interested in, as you will have to spit out lots of valuable information, for quite some time to come...
Hang-in there, whatever niche you choose, prepare to spend lots of time without seeing results, quick results do exist but are truly exceptions...