Judith Collins is the right person for this job - Don Brash

Don Brash knows a thing or two about leadership contests, and a thing or two about what's dubbed the 'worst job in politics' - Leader of the Opposition.

Dr Brash weathered leadership votes under both National and ACT and has been leader of both parties.

There are currently five candidates running for Opposition Leader: Judith Collins, Simon Bridges, Amy Adams, Mark Mitchell and Steven Joyce. Some have humorously pointed out that's nearly 10 percent of the party's 56-member caucus.

Finance spokesperson and party strategist Mr Joyce is the most recent candidate to announce he wants the job, a full week after Bill English announced his resignation. 

Dr Brash sees Mr Joyce as "the establishment candidate... the continuity candidate." 

But Dr Brash believes Mr Joyce is not the one for the job.

"None of the candidates except Judith [Collins] have been in Parliament in opposition, and being in opposition is very different to being in Government," Dr Brash said.

"Judith Collins is the right person for this job... It is the toughest job in Parliament."

Leadership contests, by their nature, can cause rifts and disagreements between MPs.

Dr Brash believes the extent of any division "depends on how the eventual leader handles his job".

That could mean rewarding your competition. In 2003, Dr Brash replaced Bill English as National Party leader. Dr Brash gave Mr English a job on the front bench.

After just one year as a Member of Parliament for National, Dr Brash won a caucus vote and was made Leader of the Opposition. He remained as leader until 2006, when he handed the reins onto John Key. He resigned from Parliament a week later, after he wasn't given any senior portfolios.

In 2011 Dr Brash took over Rodney Hide as leader of ACT, with a decision again made by caucus.

Newshub.