Donald Menken first appeared in Amazing Spider-Man #239. Donald Menken is Norman Osborn's personal assistant and employee of Oscorp. Donald's role can vary from continuity, Donald is either a loyal assistant to Norman or Harry while other times he will try and take over the company.
Greg got very little work as Donald so he does come off as generic, nothing bad but nothing to memorable about his take.
I like both Christopher and Glenn for Donald. Glenn gives a more subtle performance, pretending to look out for others while really only looking out for himself (though there is a spoiler related reason for that). Christopher continues to go through different Spider-Man characters and shows some good range, his take less subtle and more "whispery". I enjoyed his take but sometimes he is a little too whispery and makes it hard to hear.
Overall, my rank is Glenn first with CDB at a pretty good second. Greg, again, isn't bad but barley anything to work off of.