Suppose a situation when two students trying to apply for a PhD position in pure mathematics and they both have same GPA, same Rec.Letters, etc except for their published papers. Let both applicants have one paper published each, but applicant A has a "much better" research done compared to applicant B.
What makes applicant A's paper "much better"?
If it is the number of people cited his/her paper in their references it is absurd because time is the main factor of growth of its credit.
If it is the reputation of journal the paper is published it is also not a good judgement because the very same journal can contain both proof to FLT and a PhD paper.
I don't think the length of paper matters... I don't think the time that a researcher has spent matters since no one asks that...
This is a question of comparing two research paper which neither contains a solution to a famous unsolved problem; it's about papers that normally publish by students (or even professors).