Hmm... You know, that is actually a very good question! And, sadly, I don't think I really have an answer to it.
I don't actually know what my favourite video game is. There are a few that are definitely up there, but I don't think I can really pick a number one. Some of these games include:
I'm thinking it would probably be something that I've played a lot of, possibly from the Super Mario series... I don't really know tbh. But for the purpose of picking one, I'm gonna go with Super Mario Galaxy.