Which kind of blog or site will earn more in Adsense?

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I'm quite a beginner in Adsense even though I've been using it since half a year ago. From what I know, there are certain blogs or sites which can generate higher income than the rest. For example, a personal blog will not have much income as compared to a financial blog. What do you think? Which blog of yours generate higher income? Is it a niche blog? By the way, I know it requires hard work and stuff but I'm trying to do some research as to which kind of blog or site can generate higher income (definitely not personal blogs). Hopefully you guys can help out. Thanks!