Probably 4. Mismagius, Froslass, Rotom, and Giratina are all cool, and the rest is alright. The later gens have too much boring filler (though I'm not a big ghost fan), while Gens 1 and 2 don't have enough ghosts.
"Foolishness, Dante. Foolishness... Might controls everything. And without strength, you cannot protect anything. Let alone yourself."
- Vergil, DMC3