What are games most commonly let's played?

Let's played? How much does let allow you to play? Do you know what ownership is?

Mostly games with a story. The best ones are the games that give you choices, which will affect the ending. Like, Beyond 2 Souls, Heavy Rain, that kind of stuff.
You could play games like GTA V or the Sims 3. Those are interesting to watch as you can do a lot of things in those games.

Another nice game you can play is Corpse Party. As long as you have good/funny commentary, it really doesn't matter what you play.

If by most commonly let's played you mean overdone, I'd say Minecraft, Pokemon, Call of Duty, any modern FPS game really, every big name new release, most of the most famous older titles as well. So, honestly, if you want to stand out and get some fans, try to do a playthrough of something people don't already know so well or that isn't already done to death in a let's play.