Sully's fur and mammalian features suggest that he would produce red meat. His appearance and various scenes of the movie (the workout scene, ripping the scream extractor off of its mount) indicate that Sully has a muscular build, so his meat would be lean, rather tough, and have a gamey taste. Sully would taste like dry, lean beef or pork, but gamier.
Mike would not produce much edible meat -his arms and legs are thin, and the size and placement of his eye and mouth indicate that his skull makes up the majority of his head/torso, with the little remaining space needing to be devoted to essential organs. His body layout and smooth green skin suggests he is not a mammal, but his lack of scales shows he is not a reptile either. Assuming he's somewhere in between, his flesh would have a taste and texture somewhere between chicken and pork, but it would be stringy and full of gristle. There would be few good cuts of meat, and they would be small. Mike would also taste gamey, but less so than sully due to being less athletic.
In conclusion, neither would make for good meat, but Sully would produce more meat and more higher-quality cuts of meat.
