The thing is the same niche may be profitable to one but not to another marketer. So you have to pick your own niche. Don't be afraid to go into any of the three that I mentioned above especially if you have some specialized knowledge in any of them. Although they are highly competitive, if you choose the right sub-niche, you can still make money.
Traffic is another whole topic by itself. Again, one traffic source may be profitable to one but not to another. There's a lot of trial and error involved in traffic generation, so you must be prepared for that.
Thanks
I didn't find the right solution from the Internet.