A postdoc X is in the early career phase (< 6 years after PhD) in a field that needs lots of publications. X is working in a group whose leader is very famous in a slightly different but still overlapping field and very supportive of X. However, due to time constraints, the leader is unable to devote time to X's research, including extensively reviewing manuscripts. X wants to become a professor in the natural sciences.
X's current portfolio of publications includes middle-author papers and last-author papers. X is also writing a paper completely on her own, it is almost finished. This question is about this last paper.
If you are on the committee that will select X for a professorship position, what do you see as more favorable (everything else remaining the same):
Single-author paper from X
X is the first author, and the famous person is the second author
Please provide reasons for your choice.
P.S. The identity of X is completely irrelevant to answer the question.
P.P.S Negative voters please comment your grieviences.