A key moment of friction in the final face off between Morrison and Shorten

The Prime Minister was needling the Opposition Leader over his $32.1 billion change to negative gearing when the debate turned into a bigger question over the choice at this election.

Morrison had found an effective way to play on the doubts about Shorten's policy. Given a chance by moderator Sabra Lane to challenge his rival, he asked Shorten whether he could guarantee his changes would not push up rents and push down house prices.

While Shorten argued that economic analysis showed there would be no harm to prices, he stopped short of a guarantee.

"So that's a no?" Morrison asked. "No guarantee?"

"You heard the answer," Shorten replied. "You don't like our policy but that doesn't give you the right to scare Australians or ignore first home buyers."

Morrison stayed on the attack. "All I know, Bill, is that first homebuyers now have reached up to the highest level of the housing market in nine years. That's what's happened on our watch," he said.

It was at this point, 50 minutes into the hour-long debate, Shorten found a way to make a broader point about the government's record.

"Again, we hear from the government: 'nothing to see here, no problem, move along please'," Shorten said. "Climate change. Childcare affordability. First home owners. No problems in Australia. They want three more years of the last six years."

Morrison protested but Shorten was talking over him. And the Opposition Leader had delivered the line he wanted. "Three more years of the same six years."

Whatever the subject, the Prime Minister was certain to defend the status quo. Every time, Shorten could tap into a sense of dissatisfaction with the government's record.

Morrison was strongest on the tax issues at the heart of his campaign - his income tax cuts for workers and Labor's tax revenue increases.

Given the chance to ask two questions of Shorten, the Prime Minister chose superannuation and negative gearing. He also made sure to give viewers a guarantee that their private health insurance rebate would be safe under the Liberals.

"You don't grow the economy by taxing it more," Morrison said.

Shorten's two questions also told the audience what he regarded as his strength - his spending. He asked Morrison to match Labor's $2.3 billion outlay on cancer and its bigger subsidies for childcare.

In a repeat of the dynamics from the previous two debates, Morrison challenged Shorten on the cost of his climate change policy, knowing the Opposition Leader has ducked any attempt to estimate the impact of his changes on economic growth.

Shorten had prepared better this time. He disputed Morrison's ability to settle the policy and predicted the climate wars would go on under the Coalition.

When Morrison pointed out, again, that Shorten was dodging the detail about his own policies, the Labor leader argued it was a "crooked charlatan's argument" to talk about the costs. He called it a dishonest question.

On this question, as on others, both leaders stayed on their strongest ground. Morrison argued costs. Shorten argued benefits.

Those who were glued to the screens would already know which leader they were backing - and the debate would not have changed their views. Others might have switched off.

Shorten was more assured in this debate. He was ready for every question and had a quick riposte when needed. In a contrast to the way he has chipped previous hosts - like Tony Jones on the ABC's Q&A on Monday night - he focused this time on the viewers at home rather than those in the room.

This improvement helped him win the third debate.

- SMH/The Age