Well, it really depends, I can find things every generation did better than the rest.
Red/Blue/Yellow/Gold/Silver/Crystal for sheer glee and nostalgic value, with G/S/C getting bonus points for having a much bigger world and, well, fixing the absolutely broken gameplay of Gen I.
Ruby/Sapphire for being the last games I've played unspoiled by the internet, which as I've learned with D/P, really undermines the experience. Emerald also has IMO the best post-game with the Battle Frontier, to this day still feeling like the better incarnation of the concept.
HeartGold and SoulSilver for reaching (again, IMO) 4th Gen gameplay perfection and recapturing the charm of the original while still managing to feel fresh.
Black and White felt unlike any other entry in the series, and would top my list if it wasn't for a really poor post-game section.
So, in conclusion, Diamond, Pearl and Platinum were the only ones not to leave a particularly strong impression on me, although that could be in part because of how spoilered I was going into them. Watched gameplay videos and everything. Never again.
Ultimately, if I had to choose, it would be a tie between SoulSilver and Black.
Eomega123 said:
Pokemon XD Gale of Darkness for the Gamecube
Mainly because it was different. The double battles were interesting, the plot made some ammount of sense, and the villians, shocking for a Pokemon game, were COMPETENT.
Oh, yeah, also this. It's surprising how many people seem to dislike those.