Too Long; Didn't Read
The best-selling Pokémon Mystery Dungeon games are, in order:
5. Rescue Team DX
4. Gates to Infinity
3. Super Mystery Dungeon
2. Rescue Team
1. Explorers of Time, Darkness, and Sky
While the series is relatively successful, its numbers pale in comparison to the mainline Pokémon games. Hopefully, these games will be given another chance to shine with a new entry in the future.