Continuing with my going back over the previous fights to chime in with my personal opinion:
The Blob can consume material organic and inorganic alike. But after feeding, does it produce waste? I'd have to imagine yes; no known organism feeds without producing waste, which means its digestive track doesn't break its prey down on a molecular level.
The Thing, as a species, is molecular in size. The proof being that it duplicates its prey perfectly on a molecular level. Every atom of a Thing is alive and programmed to survive, adapt and duplicate. Say a Thing replicated a dog, and the Blob at that dog; it couldn't digest it down to the last atom, which means the Thing would still exist inside it. The thing could then adapt, overcome and duplicate the Blob itself.
My take: the Thing wins.