How about the ears? But if you must choose between those two, then bellybutton. Seriously, imagine, you are sticking metal through your tongue. I know a girl who has infections in her mouth just because she pierced her tongue. :P
Seriously why either? It reminds me of those primitive people who pierce their cheeks with sticks or put plates i the lips to make the huge. Or those ladies who put rings on their necks to make their necks longer. Body mutilation is gross and painful.
You know what really take courage? NOT getting a piercing! Why follow the crowd, peer pressure is bad enough without all this. And as for the risks? Well I could tell you some stories, but most already know of the common problems of "Piercings gone bad ". There's enough info on the net to back that up. :(