SPG Plat is certainly a better Elite level with more consistent and meaningful perks than Plat or Ambassador. Point earning at Plat is pretty easy with the 50% bonus and 500 amenity points.
But as both posters above comment, which works for you is driven by how much you spend and where. If you are a mid tier in spend and primary in Europe then PC makes much more sense. If spending more in Asia and the US, then Starwood offers better value. Certainly PC has better, more mid tier (i.e HI) style properties.
Also, are you interested in awards or elite benefits? That can make a difference.
Award availability in Starwood is much, much better. I have never had any problems redeeming with SPG whereas the desirable properties in PC are tough.