Source: http://www.macrumors.com/2014/03/31/ios-...

When asked about their preference for the types of games online gamers preferred, advertising supported games were chosen by the vast majority of those surveyed. 70% of respondents said they preferred free games supported by advertising and 16% preferred freemium games with the option to pay for levels in the game. Only 14% preferred online games they had to pay for to play. Gamers also prefer advertising models that give them control over their viewing. When asked if they prefer games that let them choose when and how to view ads over those that do not, 71% preferred that level of control.

Gamers also overwhelmingly preferred value exchange ads within freemium games, which allow users to play videos or view other advertisements in exchange for in-game currency or items. The recently released Disco Zoo provides a good example of such a system, rewarding players with in-game Bux for viewing short videos. The addition of free in-game items acquired through advertisements boosted time spent within games by approximately 28 percent.