First, when you decide to make your niche blog, must understand that not all niches are searched on the net. Or that some niches are already over full.
The difference between a personal blog and a general one or niche is huge. But chances to transforming your blog into a BRAND is higher to a blog of niche.
Well I think you should choose a niche on your specialization or one of your hobby. (If you are specialized in catering - write about it. If you specialize in social asistence - write about it. If you are specialized in the construction of houses - write about it. If you like flower growing like hobby - writing about it. And so on.)
In this way you can make your hobby a profession for you or your specialization a brand to others.
However, to be a brand are required and some other things.