There's an interesting discussion going on between Nigel Kearney and Lewis Holden on republican government. In a post on "The Republican Debate", Nigel argues that there are essentially three constitutional options:
1) The status quo
2) Replace the appointed Governor General with an elected President, but keep his powers and responsibilities the same. Abolish the Queen's role altogether.
3) The full republican approach with separation of the executive from the legislature, i.e. a President and Ministers who run the government, while a completely separate Parliament is responsible for making laws.
However, as I intend to explain in this post, option 2 is markedly inferior to the status quo and should not be adopted. If we don't like option 3, we should stick with the system we have. Option 2 is actually an almost perfect combination of the worst elements of both 1 and 3.
Nigel's argument for this is essentially that our current system of government - and hence a "twink republic" where the Governor-General is replaced by an elected President - requires the complete impartiality of the Head of State in deciding e.g. when or whether to dissolve Parliament or who to appoint as Prime Minister. And this cannot be assumed where a President is independently elected.
There are two obvious responses to this: firstly, that its not only elected heads of state who can run amok and abuse their power for partisan advantage, and secondly that if election is seen as compromising the impartiality of the head of state, appointment is always an option. But a more important point is that Nigel completely ignores the role of constitutional convention. The Governor-General is decidedly not free to appoint anyone they wish as Prime Minister; by convention (and pure practicality), they appoint the person who can win a vote of confidence in Parliament. In cases where it is not clear where the confidence of the House lies, then it is a matter of waiting for it to become clear, rather than stepping in and choosing a winner. Likewise, they are not free to dissolve Parliament and call elections whenever they wish; by convention, that power can be exercised only on the advice of the Prime Minister. While it's not unreasonable to worry that these conventions could break down if we change our constitutional structure, that shouldn't rule out such change. After all, we can always codify to make clear the exact circumstances in which these powers can be exercised - a move which would protect us from rogue Governors-General as well as partisan presidents. This pretty much removes any "practical disadvantages" of a twink republic, leaving us with the very real advantage - namely, no monarch.
As for the broader question of Presidential vs Parliamentary structures, TIMTOWTDI of course, but I favour a Parliamentary republic for two reasons. Firstly, it is simply easier to get there from here; the changes required are minor, and therefore more achievable (and less likely to undermine existing convention). And secondly, as Lewis alludes, for reasons of accountability. In a Parliamentary republic, the chain of accountability is perfectly clear: Cabinet is accountable to Parliament, which is accountable to the people. Contrast this with the US: who exactly is Donald Rumsfeld accountable to? Who is George Bush accountable to, particularly now that he can no longer stand for re-election? The answer in the latter case seems to be "no-one but himself". As a final note, a Presidential republic would tend to go against the grain of recent political reform in New Zealand, which has been aimed at weakening rather than strengthening the executive.