While I think the lines Don sings in ATTIG are important to the song, I've always felt Glenn was better at the soul type stuff. To me Don's voice has a rasp that works well in rock or even country, but to me Glenn's soft soul vocal on ATTIG makes it one of my favorites. Though I think Don's lines lyrically and vocally are needed. I know OOTN is a big soul type song for Don, I still feel when it comes to Memphis RnB soul stuff, Glenn's voice is my preference. Not as edgy or raspy.