All friends which are earning fro the adsence and master of this fields are welcome to share their experience with new in this field and suggest Niche / Topic of site to them.
Look for anything in the medical field, then find a niche in that. Medical always pays high PPC. IT takes research and nobody here is just going to give you a hidden gem ;-)
JMO but I try to stay away from health and legal advice niches unless I can get content written by a professional. And if you do go into that type of niche make sure you have the appropriate disclaimers. If your income will be mostly from Adsense make sure the traffic and CPC is high enough. Note also that you're looking at the CPC for the search network, you're most likely going to be using the content network which pays a bigger commission (70%) but has a significantly lower CPC. Unless you're using a search box you're on the content network. I'd also put other affiliate program ads on the website or it could get your account banned for being a MFA site, it'll lower clicks for Adsense, but you'll be safer even if you have unique content.
You need to start finding one small niche then break that down into even smaller niches and make smaller sites for each tiny niche. All the main niches like the ones being posted are so saturated and competitive that you'll be SEO'ing for awhile until you get any kind of ranking.