Its different for everyone so its hard to get really specific with you.
As far as piercings go, its a shot in the dark. Least painful tends to be ear lobes and navel and the more painful tends to be cartilage piercings and generally facial piercings. Some times its bad, other times its tolerable, it all comes down to how you handle pain and the skill of the piercer. But piercings are done and over with quickly and sore for a few days to a few weeks.
As far as most painful tattoo areas, usually anywhere close to bone, nerve endings and your joints are going to be most painful and fatty areas tend to be less painful. But no matter what it hurts even if its a little. Tattoos hurt while you get them but they don't stay sore for long, its really not that bad.
You said yourself that pain doesn't bother you, so don't make it a deciding factor in what you do to your body. If you want something, go for it.