Good grief. A poorly phrased question, and an answer that doesn't narrow the possibilities.

        *
        |
        |
        |
  *-----+

or

  +-----*
  |
  |
  |
  *

… and why?

Whichever is more pessimistic. So for the axes in this article, the first one. If you have an option on the "bad" side of the Pareto curve, you can always find an option that is better in both axes. If a new option is discovered that falls on the good side of the curve, well, then the curve needs to be updated to pass thru that new option.