Porshce already has a lot on their plate. Plus they already have ties with VW. I like Astons, but they never have seemed to get everything right. I think that BMW could instill the proper amount of care and dilligence. Toyota would take away all things Aston I think.
We CANT forget TVR ... ooh man. They would make it yet another screaming crotch rocket. I think BMW has the class, financial stability, and the success to make Astons something really great.