Quintology or Pentalogy?

Recently I was looking at the X-Men box set and saw that currently five have been released.

I had it in my head that these would be called a quintology but I have seen them being called a pentalogy.

I assume both words are interchangeable, but is one of the terms preferred over the other, or is it a matter of taste?

Pentalogy is the "correct" (as these things go) term. It comes from penta + logy which are both Greek. Quintology, on the other hand, is a mixture of Latin and Greek roots, a practice which is not linguistically kosher. Similarly, it should be tetralogy rather than quadrilogy.

Pentad and quincunx could also be used. The latter more often describes a pattern with five coplanar points, such as ones found on dominoes or dice.