i don't think either one lives up to its billing. if they would have let Wyman finish compiling The Black Box (or whatever it was called), that release would have been far more complete and satisfying. as for Rarities, there are many more b-sides and alternates and live stuff than what made the cd; live 2000lyfh '89 sinfully omitted from flashpoint, alt BS w/clapton, so many better b-sides, etc.
if they had called this release "Rarities, vol. 1" i would be more accepting of it.
forced to choose, i would say Metamorphisis lives up to its billing better (and had a far more entertaining cover, vs. the doctored wyman-less rarities cover photo).