Its all down to opinion really. You could look on this website, and see what kinds of Pokemon you can find in each region, as that could make up your mind. Alternatively, you could check out the starters and legendary Pokemon as well, as they are a big part of the plot and stories of the two games. I would personally go with SoulSilver, as it is a remake of the GBA Game Silver, and I am a big fan of the old games. It has better starters I feel, especially Totodile, and you can also walk with your Pokemon,allowing them to gain experience and you to gain items, with the Pokewalker that should come with the game. Its all up to you though really.