Now that you've analyzed the top ten competitor sites in your potential niches, think about what isn't there.
Even in a niche where there are tons of existing sites, there can be a lot of needs, wants, and interests that aren't being served.
Those information gaps can be a great angle or topic for your website.
You should now be in a good position to identify clearly where the “holes” are in the competition and in the market for each of your potential niches.
The more your analysis points to “holes” like this for any of the niches – the more likely it is that you have identified a potentially profitable niche for your authority site.
Well, you need to know that too. Unless you can come up with a unique angle, you're likely to have a harder time competing and being noticed in a niche where the competition already has everything sewn up.