Going by what I picked on my first playthroughs of these games, since I got around to using the others eventually.
Red: Charmander
Silver: Cyndaquil
Sapphire: Torchic
Diamond: Chimchar
White: Oshawott
X: Fennekin
Red: Charmander
Silver: Cyndaquil
Sapphire: Torchic
Diamond: Chimchar
White: Oshawott
X: Fennekin