First Pokemon game I ever played was "Blue" I borrowed off a friend who didn't really want it, But Silver was pretty damn fun. I had my Precious Dragonite "Shenron" trained from an egg on that, that completely drilled other players teams into the ground, I never played crystal because the cartridge was different to Silvers so my dear old "Original Gameboy" couldn't play it.
I wasn't a fan of Generation III at first because while the Johto region was a terrific advancement in the Pokemon world, Hoenn just didn't seem all that great, hell I think two of the starters look really bad, only one I don't mind is Torchic (when it becomes Blaziken)
But after grabbing Emerald on a Emulator and playing through, it really grew on me, I quite like most of the new Pokemon.
Diamond or Pearl, I plan on Buying a DS for these, I have doubts about, 99% of the pokemon I have seen in the new game they look REALLY bad, the starters just look stupid, when I get on GTS i'm dropping them immediately so I can grab a Charmander or something I'll actually enjoy.
I'll say my favorite version is Emerald due to the fact it's rather big AND it even has a legit mew hiding in the game.