I own both. The s3 has better specs but i feel the Samsung skin ruined the ease and convenience google tried to do with the ice cream sandwich update. If you want better specs get the s3 but the nexus has the better software in my opinion.
I have thought about going that route as well. Kind of test drive both and see which one I like better. I have an upgrade available and a line with a "dumb" phone on it that I could use for the Nexus. Thank you for the advice.