I like Hogue, the rubber target grips ..... I have the ones with the thumb rest but am thinking about getting the standard ones that don't have that... part that sticks out the left side.
as contender said.... really depends on which way you are leaning.... function or form.
I have Hogue cocobolo grips with thumb rest. They fit on the pistol perfectly, look great and are comfortable for me. Some folks don't like a thumb rest because they sometimes shoot with their opposite hand. On the MKIII, you can easily swap grips back and forth.