General Desktop Support question – Which user to attend to first?

This is probably an easy one but I got caught out by a question in an interview a few months back, for an IT helpdesk/desktop support role.

They asked: When several calls/jobs are logged, which should you attend to first?

I was torn between which ever technical problem I believed had the most negative effect to the operation of the business, and those jobs that had been logged first.

I chose the former, though im still not sure what the correct answer should have been – In my current position I just attend to jobs as they are handed to me by the help desk staff.