SoulSilver.
I kinda want HeartGold....whilst I'm scared of heights, I think it's better to have an epic duel atop a giant Pagoda in the middle of a major city, with a giant bird that last appeared when a pagoda burnt down, and created 3 legendaries out of 3 unknown pokemon that perished...
...when considered against battling a big, cool looking (looks cooler than Ho-oh, admittedly) bird in a cave with a waterfall, said bird having possibly lived in the now burnt down tower, and possibly possessing the ability to have created those whirlpools around the Whirl Islands.
Yeah, and the intro looks nicer.
So, in summary, picked SoulSilver, think HeartGold is better xD