McDonald for me.
Clarke is a very good player but when you make your biggest mark in a team with at least 2 other top class forwards, its always going to be easier to get a fraction more space and time. McDonald seems to be tainted by Mayo's lack of success. I don't care how exceptional you are, if the team falls apart (2004) there is very limited damage limitation you can do.
When Clarke is the main man we'll know more, he definitely has the potential to change my mind but McDonald has that something you can't teach and his physical attributes weren't/aren't as important to him as they are to Clarke