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HGSS just barely beats Plat for me since Plat has a few minor things you can't do without online (Hollowed Tower/Spiritomb) or other games (Regigigas), whereas in HGSS you can catch every legendary the game has with just yourself.
That being said, they're both incredible games and the peak of the Pokemon franchise in my eyes. Nothing will ever eclipse HGSS and Plat for me so I don't buy the new ones anymore.
BW2 and FRLG are very good too, I think.