In Fantasy Gaming, overall, the theme is what is going to make the game stand out. Choose a setting that strikes you as fun. Do you want to be a 1920's detective battling against cosmic evil? Or would you rather lead your team of adventurers through a cavernous dungeon, with danger around every turn? Or would you rather work feverishly to uncover the hidden mechanical traitor in your midst and pilot through space in a desperate attempt to reach Earth?
If your group of friends is pretty small at one gathering, a game for 2-4 players can be great, giving everyone a chance to jump in and play. On the other hand, if your game group is pretty big, then looking for a game 2-8 or even bigger would be a priority.
The other thing to consider is how long you have to play. If you are grabbing a game to take to work and play with some coworkers at lunch, you want to find one that is 30-45 minutes long. If the game is for your game night, then 1-2 hours can be great.