The Cloud Gaming Catalogue will attempt to offer a complete catalogue of every game (previously) available on these services. If you want to play a specific game, come here and look it up. You’ll see where you can play it. Or if you’re just curious which platform has the most games in the genre of your choosing, this is the place to be.cloudgamingcatalogue.com
The website is similarly useful. You can see all games available on each service, or search for a game to see which services you can play it on.
Scroll down a game page to see which services the game is available for, and also watch a conveniently located trailer for the game.