MFA (made for adsense) sites don't do well, even without competition. G knows what they are.
Niches? There's a bunch of bunches out there. The ones that do well are those that come from PASSION, EXPERIENCE, KNOWLEDGE, and AUTHORITY. Some have it, some don't.
ON THE OTHER HAND, there are a lot of niches out there where some kind of revenue can be made---but NOT the top popular this, that, or the other. Traffic might be lower ... 1,000-10,000 a month instead of 1,000,000-10,000,000 a month. Might not generate enough income to buy a mansion, but might pay all hosting/dev costs AND put a little pocket change in the bank, and do it CONSISTENTLY.
But even then, at these lesser niche tiers, you will need the same thing:
PASSION, EXPERIENCE, KNOWLEDGE, and AUTHORITY. Some have it, some don't.
The only way to find out is to give it a try.
MEANWHILE, you likely won't get many suggestions for topic/niche since everybody is doing that already and are zealously guarding any they have "discovered". However, it is pretty reasonable to say which are the MOST COMPETITIVE and difficult to get noticed: Sports, Entertainment, News, Health ... and all of these are fraught with OTHER difficulties such as COPYRIGHT, TRADEMARK, and REGISTRATION, not to mention GOVERNANCE in some cases.
One can make a living on the web, but it is NOT easy, QUICK, or GUARANTEED. It takes time, effort, money, time, more time, more effort, more money... but the biggest factor is TIME. Which means you, as the webmaster, have to have PATIENCE, Time to invest in the work, a willing attitude to work without pay, and a skill to create an internet experience that others will wish to enjoy.
It can be done.
It just cannot be done simply to make quick money with adsense.
Good luck!
