Well, I've always been very close to my parents, so "Mom" and "Dad."
Though perhaps a bit unusually, I do actually use "Papa" as well... to refer to my grandfather. Rather, to avoid having two "Grandpas" and "Grandmas," I use "Grandpa" and "Grandma" for my dad's parents, and "Nana" and "Papa" for my mom's parents (Nana passed away, however, and I call Papa's girlfriend by her first name). I'm not sure who came up with this naming scheme though, since I've been calling them that for as long as I can remember.