The ribs can be tender, but in my experience, if you're having a large piece done, you start to go numb after about 45 mins or so. The ribs are a pretty hot place for a tattoo, and easy to cover when you don't want it to show.

Hand down, the most painful place I've been tattooed is the arm pit. The shoulder cap on my right sleeve goes all the way around, and the skin under there is no fun when they run the 5 line shader over it.

I would not recommend anything in that area for a novice, unless you really dig sporting a half finished tat.