BOTH please! I love my mashed with lots of sour cream. We make ours with the skin on too, which is my absolute favorite. MMMmmmmm....love me some taters.
I LOVE twice baked. The way my mom fixes them, the potatoes get to be a light golden color on top (no extra cheese needed, that pick does NOt look yummy yum!)and the potato skin gets a bit crispy. DELISH!
By the fact that mashed are winning, I know that my father's twice bakes will need to be served more often and to more people.
The trick is to cut the taters in 1/2, bake, scoop (but don't scoop too much, or you'll tear the skin), mix the filling with extra sharp cheddar, sour cream, salt, white pepper, and butter, then put back into the skins and bake again. You want the filling to be molten, the skin to be crisp, and to never choose mashed over twice-baked again. ;^)
They both can really have almost the same ingredients and taste very similar. I am sure both can be very fattening as you add different types of cheese, bacon, sour cream, onions, garlic etc. Twice baked are my favorite when topped with cheese and bacon.