Last week Tyler Cowen drew attention, in Marginal Revolution, to Vox blogger, Dylan Matthews', opinion that "New Zealand's parliament is better designed than just about any other developed country government". Aw shucks!

Matthews argues that our unique combination of MMP, unicameral legislature and monarchy justify this conclusion.
 
He likes proportional representation because he thinks it is only fair that whomever gets the most votes should get most of the seats. However, he discounts pure party-list systems because "they can lead to a destabilizing proliferation of small parties which are able to extract promises from the bigger parties in exchange for joining their coalitions". 
 
He favours MMP because it discourages such proliferation while still ensuring that smaller parties get some say. (He does not observe that "some say" includes a fair chance of disproportionally determining whom will form the next government and the opportunity to hold the major coalition partner to ransom every time it is struggling to get a measure through parliament.)

Germany, New Zealand, Lesotho and Romania are apparently the only four countries with MMP.

What gives New Zealand the edge on this auspicious(!?) company is that it is the only one to have a unicameral parliament. Matthews has a low opinion of "meddlesome" second chambers and apparently sees the concentration of power in a single chamber as a virtue. He approvingly observes that "[l]ower houses of parliament are completely capable of drafting and passing laws of their own". 
 
Matthews' preference for a constitutional monarchy is strikingly expressed: "[m]onarchs are more effective than presidents precisely because they lack any semblance of legitimacy". His research-backed argument is that the monarch's representatives are more likely to act as a disinterested arbiter, when one is needed, than is an elected president encumbered by political baggage.

Cowen's blog expressed scepticism about MMP and suggested that New Zealand's biggest governance advantage was our limited federalism.
 
His scepticism is understandable given his co-authored 1992 analysis of constitutional arrangements in New Zealand here. One discomforting point (page 3.21) is that MMP effectively disenfranchises the many voters who don't understand the importance of the party vote.

Another disquieting tendency is for post-election coalition bargaining processes to bid up ill-targeted government spending; witness Winton Peter's "Gold Card" for the elderly. Economists Torsten Persson and Guido Tabellini found in the early 2000s that government spending tended to be higher by 5% of GDP under proportional voting systems. That's a whopping tax increase.