Your username should depend or your own likes and dislikes; for instance, the reason I picked "Aquabreeze" back in the day was because I was (and still am) a fan of Avatar: The Last Airbender, but I couldn't decide whether I wanted to be a waterbender or an airbender. So I combined water- also known as aqua- with air- breeze- and voila! Take some stuff that you like about the game, or something that describes you, and combine it, and look for synonyms of that thing if the name is already taken- or add a few numbers at the end, like your birth year or completely random numbers (the 87 just sounded cool I don't know) if you're really attached to the username.
Minecraft is one of my all-time favorite games.