A:
I've upgraded from a Wacom Intuos 4 Medium. In reviewing the differences, between the Pro Medium and the Pro Small, the only differences I can see is the addition of 2 more buttons in the medium. but I am thoroughly enjoying the small as the customization with the pinnable radial menus more than make up for the loss of 2 buttons. The pens are exactly the same for both tablets and are even the same pen used from the intuos 4.
I also found that with a medium tablet, I was only drawing within a certain area on the middle of the pad, so for me the small works great. and it's easier to pack up and travel with, or store on the side of the desk when not in use.