There's so many possible niches and so many variables that it's unproductive to tell you a single niche, because once you understand how to find one (it's really easy) then you won't have that question again.
Niche choices can be seasonal or year round. For example, you can make a website about easter products that obviously wouldn't do well in September, but you could end up making a lot of money during easter season.
Like I've already mentioned, you can look through Amazon best selling products and get ideas from there. Let me do that right now just to give you an example.
Okay, here's an Omaker M4 Portable Bluetooth Speaker. If you're an audiophile, you could easily have some fun with this product. If not, it's still a good item to promote.
Now from this product, there's lots of things you can stem from. Make a niche about bluebooth products, about speakers, about music listening devices in general. You can even go a bit broader and make your website about what does good music sound like (music theory). These are just ideas off the top of my head.
For this, we'll say the niche we'll be testing is "bluetooth speakers".
Next, use a keyword tool to search up products related to bluetooth speakers.
I'm not using my own tool for this, but here's some ideas I'd enter in:
best bluetooth speakers 2017
best bluetooth speakers
where do i buy bluetooth speakers
should i get a bluetooth speaker
what is a bluetooth speaker
and so on. After analyzing the numbers for these, you want to have about less than 100 competitive websites while still getting at least hundreds of searches per month. If there's too much competition or not enough searches per month, try out a new idea for a niche (e.g. "bluetooth products" instead of "bluetooth speakers").
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