Pros and cons: Who will be National's next leader?

Bill English has confirmed he will step down as National's leader.

The party's caucus will elect the next leader - and English says he will cast a vote, but has stopped well short of endorsing a successor.

"And I look forward to them coming to me to ask for it after years of having to ask for it myself."

Claire Trevett weighs the pros and cons of the potential contenders for the role.

Judith Collins:

Pros: Definitely has the 'mongrel' required for Opposition and the ambition to match it. Not squeamish about tackling Prime Minister Jacinda Ardern where others might hold their punches. Has support in National circles as one of its right wing.

Judith Collins: "Has the mongrel required."

Cons: Has some political baggage and is polarising. May not be able to secure confidence of whole caucus - carries the risk of dividing caucus.

Simon Bridges

Simon Bridges: "Would be the first Maori PM, if he made it that far."

Pros: Young enough to be 'new generation' change but experienced enough to know what he's doing. Well versed on the economy and regions. Aggressive in Opposition. Would be first Maori Prime Minister if he made it that far.

Cons: Strong accent, wears ambition too openly and treads fine line between holding government to account and being obstructive for the sake of it. Opinion of him is divided in caucus.

Mark Mitchell

Pros: Former security contractor in Iraq is likely the only politician who has shot at other people, but is well-liked and even tempered. Works hard on relations with media and other politicians.

Believes National should mend bridges with NZ First - and is one of the best placed to do so. No political baggage.

Mark Mitchell: "Likely the only politician who has shot at other people."

Cons: Intellectual rigour unknown, not yet seen as a heavyweight. Low public profile. Has been tested under fire literally - but not yet in politics. Then again, neither were John Key or Jacinda Ardern.

Amy Adams

Pros: A steady hand with brains and a measured approach. Was one of former PM John Key's favourites. Impressive in her ministerial portfolios.

Amy Adams: "One of former PM John Key's favourites."

Cons: Low profile in Opposition and may struggle with the likeability factor. Is also yet to show if she has the 'mongrel' required for the job. May be consigned to good deputy material.

Dr Jonathan Coleman

Pros: Combative, which is good for Opposition. Not ideological and showed guts standing for the leadership before.

Jonathan Coleman: "Combative."

Cons: Has little support and is unlikely to build it. Not popular enough in caucus or the wider public.

Nikki Kaye

Pros: One of National's socially liberal MPs, like Bridges Kaye represents change but has experience. High public profile, especially in Auckland. Knows her enemy well, having beaten Jacinda Ardern in Auckland Central. Has adjusted quickly to Opposition.

Nikki Kaye: "Knows her enemy well, having beaten Jacinda Ardern in Auckland Central."

Cons: Socially liberal views could make National's base nervous. Doubtful whether she could muster enough support to beat Bridges and Collins.