I don't think it is really possible to compare the two without skewing it one way or the other.
I find it pretty close to impossible to have a conversation about relationship structure (monogamy vs. nonmonogamy) without emotions getting involved and without delving into the pros and cons without being attached to the outcome, it isn't possible to say which would be better if all other factors were the same.
For each individual, this discussion could be had based on their personal experiences, beliefs, feelings, situations, etc. but to say monogamy is always better or polyamory is always better in general... Not possible.
For all we know there could be underlying psychological or physical benefits to one over the other on an almost universal scale. Who's to say?