OU, NU, and LC. OU has a lot of popular pokemon, and it's a battle of the non-legendary (most of the time) powerhouses. NU is really fun since the technique to play in the tier is much different from OU. It's also fun to be able to use weak/rarely seen pokemon in a useful way. LC is extremely intense, competitive, and fun with level 5 monsters that have extreme potential. There are so many added strategies that come with unevolved level 5 pokemon. These 3 are really fun, and are my favorites.