There’s three good niches that will always remain popular for as long as human civilization exists. Those three niches are: wealth, health and relationships. Think about it, people are always interested in making money (wealth) and are more than willing to learn how to. Then you have health – people are always wanting to know how to lose weight, and so on. Relationships …well, those will always be around. Those are three long-term niches that you should look into.
A perfect example of this would be if you were trying to rank for something like “blogging” or “how to make money with a blog”. The two search phrases are similar but completely different in nature. There is no way to know what someone wants when they search for “blogging”, however if someone is searching for “how to make money with a blog”, it’s quite obvious.
For example, if I talk about how cool a product is, and then you find out that I’m an affiliate for them, wouldn’t you as a conscientious observer become skeptical as to whether my information is biased, if perhaps I’m only saying how cool something is because I can get paid for it? Wouldn’t that make you question my integrity with other things I say as well?