Steam has revealed their annual earners list which is the top 100 best selling games on the Steam platform, the way it works is that there are 4 ranks: Platinum, Gold, Silver and Bronze with each of the top 100 games being placed in each rank with the Platinum category having 12 games meaning these are officially the top 12 bestselling games on Steam but no one knows for sure how much money each game has made or which is the biggest earner of them all. (There are 12 games in the Gold category, 16 games in the Silver category and 60 in the Bronze category)
The top selling games on Steam for 2017 in no particular order are: Rainbow Six Siege, Divinity Original Sin 2, Grand Theft Auto V, H1Z1, Warframe, Dota 2, Counter Strike, Rocket League, Ghost Recon: Wildlands, PUBG Battlegrounds, The Witcher 3: Wild Hunt and Ark: Survival Evolved. The games are measured by all their revenues streams such as the cost of buying the game (Warframe is the only free to play game in the Platinum category), DLCs and microtransactions.
Here is the full list: Link