User blog comment:TerrariamcSwaggins/Hey guys, Goblin Army, Pirate Invasion, or Frost Legion. Which is your favorite?/@comment-1466854-20131121085143

Goblin's easy, and can be amusing to squish with odd weapons, but that's about it. Frost would be fun if not for the post-fight cleanup work. I get sick of having to remove all the snow they leave around my structures. Pirate wins by default, but it also is the only one of the three with worthwhile loot.

Also, Pumpkin Moon also doesn't qualify in this list. It's not an invasion, can't occur naturally, functions on a time frame instead of a kill count, isn't affected directly by player count... it's a very different beast, though admittedly a fun one.