15" rMBP, 16GB, at least 512GB SSD (will go higher if price difference is small enough).
When I purchased my late '08 MBP, 2GB was plenty. A few years later, going to 8GB (max capacity) helped a lot, as I occassionally need more than 4GB of RAM. Since the RAM likely won't be upgradeable on the Haswell rMBP's and I expect to have this machine for several years, I'm going to 16GB to ensure that I won't "outgrow" an 8GB machine.
When I purchased my late '08 MBP, 2GB was plenty. A few years later, going to 8GB (max capacity) helped a lot, as I occassionally need more than 4GB of RAM. Since the RAM likely won't be upgradeable on the Haswell rMBP's and I expect to have this machine for several years, I'm going to 16GB to ensure that I won't "outgrow" an 8GB machine.