Today, we will learn who the 13th leader of the National Party is going to be.

Simon Bridges, Amy Adams, Steven Joyce, Judith Collins and Mark Mitchell are all vying to be Bill English’s replacement.

The party caucus will make their decision this morning, and all the talk is it's a two-horse race between Bridges and Adams.

Former National Leader Don Brash and former National PR Man Ben Thomas joined Mike Hosking to share their takes on who will win.

Brash says the party must remember it s choosing a leader of the Opposition rather than a Prime Minister.

" The Leader of the Opposition is the toughest job in Parliament. You're expected to have an informed opinion on everything the Prime Minister has an opinion on, and you only have a small fraction of her resources."

Both Thomas and Brash says Judith Collins is the best person for the role, but in reality, it's likely to be Simon Bridges who wins.

Thomas says the party should consider it might be shut out until the 2023 election.

"What you might be asking is can Simon Bridges lead the Opposition for six years and then enter into Government? That's a difficult call and we've seen the problems Labour have had in that respect in Opposition."

Thomas says staying leader, and uniting the party, will be tough with four failed leadership contenders and the party's old guard waning.

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