Time played could be inflated though, if you have a game that uses time as score, and just sit on the page, you get time played.
Also some games allow you to play longer, like a role playing game, versus a speed based game like a typing skill game.
I would pick a game a week, and put that as the game to play, and whoever was on top at the end of the week, would win, or a category, like only count the games in that category towards the player of the week/month.