You may want to define some clear vendor evaluation criteria, otherwise it's tough to say which is "best". Depending on where your users are concentrated geographically, what type of app/game you are looking to monetize, what types of ad formats would make sense for your game/app, # MAUs, # apps you need to monetize with ads, # ad networks SDKs you want/need to include, whether you want to sell traffic direct to advertisers etc. - there may be a different answer.