In honest, stream games that you like. But if you want my opinion and what games I'd stream, this is my list.
1. # Minecraft ( Can be really entertaining and you have loads of things you could do. This is also a fun game with friends so starting a SMP ( Survival Multiplayer ) server with friends would be loads of friends meaning you could get content for yourself and others in the process of doing this. Also the amount of servers and game-modes that they can offer is also an option either being solo or having friends or people to do it with. )
2. # OSU ( This game is really dependent on the user as this game isn't really a game that all like. But I really love this game myself and I would personally stream this. There is also multiplayer lobbies for which you could play with viewers or friends and or both. )
3. # COD ( Now I'm not going to specify any Call Of Duty game because of the remaster for MW2 I believe? Or possibly the newer game and not a remaster but either way yeah. These game titles have loads of content you could do and you could also have tons of fun.
There are a ton of single player games you could possibly stream and have fun with, but those are my top three.