It's one thing having an offer you can't refuse.

It's quite another having two offers you can't refuse.

And that is the handy position that New Zealand First appears to be in as continues to ratchet up twin parallel coalition agreements with National and Labour.

It is plausible that both sets of policy agreements are acceptable in different ways.

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Labour is likely to be more agreeable to New Zealand First policies simply because they have more in common.

But National has greater experience in deal-making with coalition partners, and with the weight of nine years in Government, is likely to have come up with a muscular and equally attractive agreement.

The decision, when it is finally made, may come down to other factors, including leader to leader relationships, and an assessment of how each party would affect New Zealand First's survivability in the 2020 election.

Which ever party leads the Government, New Zealand First could expect an unsolicited electoral arrangement in 2020 to assist the party's survival in Northland or Whangarei - which would never be spoken of.

It would simply be in both parties' interests.

The relationship between Peters and English or Ardern could be a crucial factor.

It could be more difficult for Peters to establish a relationship of trust with English, who was deputy leader when National ruled out Peters in 2008 because it didn't trust him.

But English has just as much reason to distrust Peters than vice-versa after Peters' personal attacks over the saga of Glenys Dickson, the former electoral agent of himself and Todd Barclay, in the dying months of the last Parliament.

These relationships don't have to be friendships. They have to be professional.

English is a proven manager of relationships in Government, not just as Finance Minister, and did a lot of the heavy lifting with support partners over the past nine years.

The advantage for Jacinda Ardern is that she and Peters don't have an established relationship.

They have no baggage. But the prospect of installing an inexperienced young leader as Prime Minister would also be a huge step for Peters.

The workload would be enormous for her, managing a party, a government, and a coalition relationship after just two and a half months as Labour leader.

The risk for Peters would be huge.

In the end, it may have to come to down to ministerial positions.