As far as I know, Google Adsense is by far the most lucrative ad network (unless you own a big website that can get an individual advertising deal) - meaning you'll be earning pocket change in comparison, no matter where you get approved at.
I've only personally tried Chitika, and the drop in my ad income was so steep, that I switched back to Adsense after just a couple of days.
So my vote definitely goes in favor of raising the quality of your website until it passes the criteria for an Adsense account.
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