Aptitude and Interest, both are important. In case, a student has aptitude, but no interest in the chosen subject - his/her performance will be poor. Similarly, if he/she has interest, but lacks in aptitude for the chosen subject, then also his/her performance will be poor.
What should be considered first when recruiting students for a university?
It is hard to put first, second, third etc. in sequence whereby some attributes need to be evaluated at the same time by the university - the more time spent & details the university is assessing the following, better will be the outcome:
Competency (why important - only competent students can accomplish what they are studying).
Interest / Passion (why important - this will motivate the student to excel i.e when you passionate on what you are learning / studying, you will do your extra best).
Attitude i.e. covering other attributes like ambition, willingness to learn, diligence, perseverance etc. (why important - positive attitude can sustain the student even though they might not be competent in certain areas initially, but through their diligence / perseverance, they can still be successful in completing the course).
Note: above attributes also subject to other factors like assessor's ability, courses availability / limited seats, quota etc.
The relevant subjects competence is more important than the other criteria such as intelligence (general reasoning ability), aptitude (ability to learn), motivation (enthusiasm to study) and passion for continuous learning. This will ensure that the student will be able to deliver learning outcomes.
I would say all the above are of importance but each subject area needs to rate importance of each according to not only order of relevance for the subject area but also the qualities desired for a practitioner after completing the studies-(acquisition of some qualities can also be included in the studies, however)