I'm actually playing both SoulSilver and Black more or less at the same time, though I'm playing Black more often - it's my first playthrough for both. (I've had SoulSilver almost a year, but I'm stalled before beating Red (because his team is in the 80s and only one of mine is in the 60s) and grinding is aggravating at that level, so I don't feel like playing it as often as I feel like playing Black.)