Need to get rid of a phone - Galaxy S3 vs Nexus 4 - which one should I sell?

I have a 4 month old Samsung Galaxy S3 (Blue 16 GB) and a two week old Nexus 4 (16 GB). Both phones look flawless on the outside and pretty much new. However I need to get rid of one of the phones.

Questions:

1. Which phone is more future proof going forward - not just in terms of SW updates, but hardware also?

2. Which phone could fetch me more money?

3. Which phone would you sell?