I have a Minecraft let's play series on YouTube. Well, You shouldn't focus on what's popular, you should play games you enjoy but, to answer your question some popular games are of course Black Ops 2, Battlefield 3, and some other FPS games. Hoped this helped!
Play something new and indie. Don't do Minecraft. It has WAY too many already for you to get many subscribers and views off of it. With something new and indie? If someone searches for footage of it you will really be their only choice. Thus more views and stuff.
Lawbreakers. I'm mostly saying this so my que time gets reduced.
It's also fun to play tho.
Edit: Whoa golly, didn't realize this was necro'd.
Rise from your grave!
I can sympathize with your intentions, as I tried the same thing with a few other lightly populated games via raw gameplay videos. I figure that unless one has an established subscriber base, one's best bet for attracting folks to a game is simply to provide a representative view of the gameplay so prospective players can discern whether they want to get involved with a game.