Winston Peters has announced his post-election coalition preferences: as in 2005, he will negotiate first with the largest party. It's a perfectly reasonable position, which will give some certainty to voters about what the possible outcome might be (assuming, of course, that Winston makes it back in. He might not - on current polling, NZ First won't make the 5% barrier, and Winston is not guaranteed to win an electorate). It is also a fairly good strategy to maximise NZ First's leverage.
NZ First has learned from its disastrous 1996 coalition deal with National. Rather than push for a "cast iron" coalition agreement, with an agreed policy platform from the outset, in 2005 NZ First went with a much looser arrangement [PDF], promising confidence and supply in exchange for "consultation" and a limited set of policy concessions (most of which were "we'll look at it"). Sure, Winston is in outside Cabinet, but the rest of his party isn't, and they have a free hand to criticise the government. They also have an almost entirely free hand on legislative matters, forcing the government to bargain with them on a case-by-case basis for support on legislation. While they've been quite reasonable about this, offering support by default unless they have a serious problem with a bill, the fact remains that they effectively have a veto on legislation. And the mere possibility of that has significantly constrained the government's program.
This has worked because Labour is used to MMP, used to compromise, and is able to moderate its policy programme while finding areas of common ground it can work with other parties on (e.g. kiwisaver). But I can't imagine it working so well with National, firstly, because the party has not adapted well to MMP (it still has an arrogant "born to rule" attitude, and has systematically failed to exploit the government's weak position this term by building coalitions and running its own legislative agenda). And secondly, because of the policies it wishes to pursue. There's a much wider gulf between NZ First and National than between NZ First and Labour, and I can't really see Winston voting for privatisation, superannuation cuts, and looting the state, no matter how many baubles he's offered. If forced to rely on NZ First, National may find itself government, but unable to enact their core election promises or policy platform outside of law and order. The net result is likely to be hissy-fits and threats of an early election to "gain a mandate".
The same analysis applies to either of National's other possible partners across the centreline, except there the policy gap is even wider. Basically, if National has to rely on anyone other than ACT or Peter Dunne - in other words, if they fail to score more than 47% of the vote - they're crippled.
