Well, the game won't be released in Japan until September, meaning that North America will be waiting for at least one solid year. I'd reccomend making regular stops by
Serebii.net for constantly-updated word on all things Pokemon, not to mention a thorough rundown on the basics of series.
In other words, just pick your favourite colour of the two. In keeping with personal tradition, I'll be purchasing the less-popular title in the pair, presumably Silver.
Sorry to use Crunch on your bubble, FBM, but Celebi will almost certainly be this generation's token downloadable Pocket Monster.