Thats tough, I don't know Silverlight but I know its still far from saturated into the market. If you are focusing on web, then I'd still do AS3, no question. If you want hardware support, I don't know how they compare, but I would look at the hardware you want to support, and see what their roadmap is.
jeremy - gnomeontherun
Educated questions often get educated answers, and simple questions often get simple answers.