So first decide what's the market for your book. You'll need that information for your proposal, which MUST be completed before any agent or editor will even speak with you. Publishers want specifics. In this day and time, you, the author, will be largely responsible for promoting your work, so you better know how, where, to whom, when, and why the book will be bought. Which scenario will prove more beneficial to you might be surprising, kinda like it seems a paradox that all the car dealers in one county sit on the same block.
Competition can be very good for sales.
Of course, TOO much competition kills you before you get in the door. While publishing claims to hate Ph.D.s, such is not really the case. You don't HAVE to have the letters behind your name, but you do have to know your stuff. In other words, even if you have no degree in Homemaking Ed., you better be able to convince an agent, editor, publisher, and readers that you know how to sew the skirt. Knowing the why of it will cause you to refine your proposal, while answering many of the larger, AND smaller questions.