The name of the field that compares moral systems and asks question about the nature of ethics in this way is metaethics (SEP entry).
There's three related meta-ethical questions that affect the answer to your question:
- Is there moral realism or not?
- Assuming it exists, can we have access to this moral reality?
- Assuming it exists and that we have epistemic access to it, is it the sort of thing that is comparable in kind?
None of these are clearly resolved in some sort of absolute way for philosophy.
Is there moral realism or not?
The question here is whether we believe there are facts about morality, i.e. claims that are genuinely true or false about our moral actions. Are certain things good or bad in fact or are they merely good or bad as a matter of perspective?
The vast majority of moral philosophers historically are moral realists -- Plato, Aristotle, Augustine, Aquinas, Locke, Wolff, Kant, Hegel (see below), Mill. This is not without exception -- I read Hume as not being a moral realist or at least a moral skeptic [next issue].
The contemporary picture is cloudier. Several philosophers have mounted arguments against moral realism -- Richard Rorty (at times), Jacques Derrida (at times), David Wong , J. David Velleman, Gil Harman, etc.
Assuming moral realism, can we access this moral reality?
Just because something is real does not mean we can know it. This is an argument which goes back at least to Socrates (and is part of the difference between Plato and Socrates). Hume is definitely a moral skeptic. A moral skeptic can but need not deny there is a moral reality. Instead, they stake their claim on our inability to know these things.
Assuming it exists and that we have epistemic access to it, is it the sort of thing that is comparable in kind?
Here, the thing is that even if moral reality exists and we can know it, it may be the case that it's not the sort of thing that can be subject to comparison. The idea that it's comparable is most compatible with consequentialist views where there is something quantitative that we are minimising or maximising (e.g. Utilitarianism).
Quote from Hegel in support of moral realism:
for to describe evil as hypocrisy implies that certain actions are in and for themselves misdemeanours, vices, and crimes, and that the perpetrator is necessarily aware of them as such insofar as he knows and acknowledges the principles and outward acts of piety and integrity [Rechtlichkeit] even within the pretence in whose interest he abuses them (Philosophy of Right, Section 140(e))