Think what sales will make a lot of backs for advertiser. For example, mortgage client will make lots of cash to bank.
Some of the profitable niches include insurance, financial services, and education. There are many niches where advertisers are willing to pay big bucks for clicks in Google (and of course this contributes to high adsense earnings as well.) Just use the google keyword tool to see what the estimated cost per click is, and this should be a fairly reliable indicator of what should pay out well in adsense.
I think if you want to earn with adsense.. got for finance, real estate.. health and beauty they are the best paying niche so far..
I think you should get really niche specific, don't just write about an I phone for example, include a specific type. Another example would be not to write about say... fat loss for example, but some sort of specific aspect of it, like a program or product. Focus on really tight focused longtail keywords that still get alot of searches.
You have to find out what you, yourself are interested in ? Any niche whatever you feel nice to talk about would be best for you as you will have lot of amazing stuff to talk about
Finance, money is the best earning i guess, followed by Domains and web hosting niche , followed by MEsothelioma regards Joshu