For me the belly is the best area by far. Once in a while it hurts, but ususally I don't feel much. It helps that I have an ample belly who knew it would come in handy someday..lol.
As far as the areas on the diagrams we are given.. I've asked my nurse about other spots and she told me that not all areas of the body are options because of differences in absorption. Some sites are better, some may not be good at all.....
It would probably be good to ask before picking out new places not on the diagram. I wanted to do my inner thigh instead of outer, and she said not to.