Emerald, Platinum, Heart Gold and all the Pokemon Ranger games. :D
Emerald because it's the remake of my very first Pokemon games (R/S) and honestly I loved the storyline, the characters and all the amazing new features. As for Platinum, for very shallow reasons: (1) Looker/Handsome is in it, and (2) Giratina is in it and very involved in the story. :D The Reverse World is win. Finally, I never played G/S/C, but Pokemon Heart Gold is LOVE LOVE LOVE. Although the Pokemon choices aren't great, and the GLs weren't that challenging, I have a lot of fun playing it, and all the mythology surrounding Ho-Oh is epic win. As for Pokemon Ranger... well, actually, I have yet to play Shadows of Almia and Guardian Signs but I'm gonna get them eventually and if they're anything like the original Pokemon Ranger game, I will have a lot of fun with them. :D