We strongly discourage link-only answers for several reasons, one of which is that if/when the link breaks or rots the answer becomes useless and future readers are left with a non-answer.
In this Space SE answer (using because it's a good and recent example) there are three scholarly articles cited. The OP linked to PDFs, I modified the links to make them the source/abstract page rather than the PDF, and the OP changed them back to the PDF links again.
I'm asking this question here because there are more users familiar with linking to scholarly papers here than there, and where this is done in answers a lot more frequently.
Question: Should we link to the PDF or to the abstract or source page for scholarly references?
My suggested (and rejected) alternatives: