Get Blue
Yellow
(you can get crystal if you want one of those games)
I'd say Sapphire instead of Ruby, but I liked kyogre more
EDIT: Leaf green or fire read, if you want to get a newer version of the originals for better graphics, but its not necessary uinless you want one of each pair/triplet games.
Diamond (i got pearl and Palkia is a much poorer legendary then Dialga)
HeartGold (I like the option of Ho-oh first then a strong Lugia later where the training is done for you)
And then the new one depends if you like a more nature theme or industrial.
Really none of the games are different from each other within their generations, you just have to think about which pokemon you want, since each has version exclusives. And you can pretty much substitute Emerald for Ruby or Sapphire since you can get Groudon, Kyorge, and Rayquaza in one game in Emerald.