Resident Let's Player here yo.
I will always suggest you find a game you know well enough, can talk over, basically are comfortable with.
As you're just starting out, I'd say go for something relatively short.
If you want any advice, help, or just to talk, send me a PM.
When it comes to LPING, you'll want to find something without too much grinding (IE: Pokemon, FF) and just enough story, so that commentary won't have to be the biggest part of it. Of course, you may find you have a natural presence that attracts people instead. Just keep that in mind.
If you do a game like pokemon or that sort, just keep in mind your viewer won't want to watch you run back and forth in the tall grass, etc etc.
My dad is a huge connoisseur of LPs, these folks are pretty right so far. Keep in mind that the game preferably is one you have played with appealing visuals, that you may know very well or have the inside scoop on. - Gorntrex