I had my tongue, eyebrow, nipple and upper cartilege (ear) done... all gone now but the nipple piercing. Of all of them, I'd have to say the most painful one had to be the ear. The eyebrow was surprisingly painless, and in the two years I had it, didn't migrate at all.
Also, I've had the nipple done since 1994, and hasn't migrated one bit. Rejection is a product of proper placement, and the specific body's reaction to the piercing (I've heard).
Enjoy the eyebrow if you get it done, but make sure you don't sleep on that side for a while, or it'll "sit up" on your face forever
