My one and only altitude deviation came when I was PF. We were cleared to 350. ATC ammended the clearance. I dialed in 320. The PM read back the clearance to ATC, then verified my 320 selection. When we climbed through 305 we were asked to state our altitude followed by an immediate right 90° turn. In the ASAP, both of stated we were certain the clearance was 320. They kindly replayed the tape, and the PM very cleanly responded to ATC to maintain FL300. I believe, if the PM set the altitude, this deviation would not have occured. My company still has the PF set the altitude when the autopilot is on, but if we switched, I would understand why.