Hi Javanshir,
Before choosing an ad network, I'd suggest getting a better understanding of the best ad unit for your users during that moment. If you don't know, look in to using a platform that gives you the flexibility to easily test mutliple ad units and multiple networks without having to go through the headache of integrating and removing mutiple SDKs. Mediaiton layers can help with this.
Happy to chat if you'd like more information.
skype: garethleeatwork