"Name MC's who are average but shine on others' songs"
This post is inspired by Memphis Bleek. He seemed to come off well when he was featured on other people's tracks (It's Alright, 'Round Here, others) but could never translate that energy to his own full-length albums.
Inspectah Deck qualifies for me as well, but I know some people really like his on LP and may feel his name shouldn't be included with Bleek's.