Well I'd suggest the hydra network, they typically have a lot of offers, are reliable, and are easy to sign up for. But in the end you should get involved in all of them if you can.
Clickbooth differentiates itself from other networks by offering its partners internal testing in order to maximize returns. Clickbooth takes it upon themselves to ensure each campaign is optimized to its full potential before it’s given to publishers.
They also have an awesome referral program! Use the Clickbooth Publisher Referral campaign to receive 2% gross referral credit FOR LIFE! Plus, you receive an additional $10 bonus for every affiliate referred!
If you are interested in CPA networks, Clickbooth is a great place to start or continue maximizing your revenue!
Read up on clickbooth before you join and/or start sending them traffic. I have no personal experience with them, but after reading problems others have had I dont think I will either. I vote for hydra and neverblue.