Hello! What niches do you use for you sites. and what`s the medium ppc ? I have a site who have ppc fluctuation from 0.02 $ to 0.90$! Why ?
All the niche are best niche if the site itself is quality site By the way, There are many factors determine the price of an ad, not only the keyword More than conversion rate goes into determining the price of an ad: the advertiser's bid, the quality of the ad, the other ads competing for the space, the start or end of an ad campaign, and other advertiser fluctuations.
there will be always a fluctuation in the pay per click for any niche because there are many factors that affect on the ppc not only the niche!
You can try to go through the Google's keyword price viewer and a see a good paying niche for you. Of course... you need a good quality site in the end to get your traffic and visitors.
I've optimized sites for "three legged pedophile parrots who can't speak Chinese" and it worked like a charm, got a bunch of $17.32 clicks
Take a look at this recent article with the current top 20 highest paying keywords/niches. Should give you an idea of where to aim!