I've worked with RollerAds for a few months now, and it's been my main source for push.
It's really nice for Push Traffic, not so much for Pop though...
It's definitely easier to get your ads approved than Propeller Ads.
The platform looks nice and is easy to use.
You can target your traffic very precisely, and they allow CPA and auto rules optimization.
The volume is not that bad to be fair.
The staff is reactive.
You can pay with Paypal and Credit Card.
I think it is worth to give it a try!