Are orbitals always filled in from closest to nucleus to farthest away? In which orbital, 4f or 6s, would an electron have a greater likelihood of being near the nucleus.

I figured that the 6s would be closest, since it is filled in first when using the Aufbau principle.
However, does that necessarily imply that it is closer to the nucleus? Or would 4f be closer, since its principal quantum number is smaller?
As you have studied for the quiz, you should know the expected answer.

In full-scope reality, the question has nothing to do with the two explanations you offered, but with the shape of atomic orbitals:



Radial distribution of selected orbitals in $\ce{Sm^{3+}}$, http://pubs.rsc.org/en/content/articlehtml/2004/dt/b407173e