I personally like Pokemon Emerald the best, mostly because of the Magma/Aqua storyline. Team Rocket and Team Galactic always have the same goals, take over the world, blah blah blah. But Teams Magma and Aqua didn't want to rule the world, just change it for the benefit of people and Pokemon (or so they thought). Their methods may have been wrong, but their intentions were good and believable. You might even call them the eco-terrorists of the Pokemon world.
Also I liked the Battle Frontier. There was so much stuff you could do there.
Pokemon Pearl was ok, I liked the variety of Pokemon and attacks that it offered, and I also enjoyed the fact that the story goes on for a little while even after you beat the Pokemon League.
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"Yeah, so this one time, I tried playing poker with tarot cards... got a full house, and about four people died." ~ Unknown comedian
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