pop works good, as you can get it in cheap rate and you can spread words about your site in very low cost, and if your site has good content and its attractive than defiantly people would want visit itI use some CPV network and get good response
GPT is simple waste of time, because in most you will never able to make enough to get cashout, because every site will have minimum amount to receive payment, and most of those gpt sites are scams once you reach some $$ they will either suspend your accont, or they will delete you