Papaya ads provides one of the best services in the market and very cost friendly. Their team is very result oriented. I have been associated with them for past few months and it worked really well for me. Review collected by and hosted on G2.com.

A few downsides I noticed is that they need more budget to get started with. Also they work really well with broad audience but when it comes to small audience size, something goes wrong. Review collected by and hosted on G2.com.