I'm strongly considering buying both HeartGold and SoulSilver - HeartGold for my main game, and SoulSilver to replay as much as I want.
In HeartGold (in which I'll be playing as Soul), I'm starting with Cyndaquil. This is the starter I usually pick in the second-gen games, though I have started with Chikorita before, too.
In SoulSilver (in which I'll be playing as Gold), I'm thinking of doing something I've never done before, and starting with Totodile. I've raised Cyndaquil and Chikorita before, but never Totodile. However, in the third and fourth generation games, my dominant starters were the water-types. I've come to really like the water-type starters, so I think Totodile will be great to train.