For Labor Premier Jay Weatherill it's about fulfilling the government's promise of transforming the state into a global innovator, embracing new technologies to create the jobs of the future.

For SA-BEST leader and former senator Nick Xenophon, it's about being a disruptor, with the power and influence to set a new agenda in state politics.

But just who will prevail on Saturday night after more than one million voters have had their say remains very much up for grabs.

Look back to 2014 and Marshall was poised to end 12 years of Labor rule, heading into an election he, and most political pundits, expected him to win.

In one sense he did, the Liberals finishing well ahead on the popular vote.

But he failed where it counted. The party was unable to convince enough undecided voters in key seats, those that Labor successfully defended with a brand of local politics and campaigning that has become the hallmark of its election strategy.

Less than a year out from this election, Marshall was once again poised to seize office.

The Labor government was struggling with surging power prices, the aftermath of the infamous statewide blackout, together with issues surrounding the failed Oakden nursing home and the protection of vulnerable children in state care.

But that all changed on a warm day in October 2017, with Xenophon's shock announcement he was quitting federal politics and coming home.

He planned to win a seat in state parliament and have his party win enough seats to hold the balance of power.

In a line he had clearly rehearsed he declared politics in SA was broken. The state was "politically bankrupt".

"We have a government that deserves to lose and an opposition that doesn't deserve to win," he said.

Xenophon's enduring popularity and ability to tap into voter discontent with the two major parties turned the battle for office in SA on its head.

Though he had no other candidates at the time, there was, and still is to some extent, a groundswell of support for the man seen by many to be a truly honest player and a champion of the people.

An opinion poll in December had SA-BEST leading both the major parties on the primary vote and miles in front of the Labor and Liberal leaders as preferred premier.

Interestingly, the media placed him on an equal footing with both Premier Weatherill and Marshall.

He sat alongside them at leaders' debates and observers quickly bought into his concept that this election would be, for the first time in living memory, a genuine three-way contest.

But it hasn't exactly played out that way.

Amid suggestions he has spread himself too thin, by seeking to contest 36 of the 47 seats, his campaign faltered and support has slipped.

In the most recent poll in March, SA-BEST trailed a distant third behind the Liberals and Labor, and Xenophon only just shaded Weatherill as the best person to lead the state.

It seemed the bright Xenophon flame was at risk of being snuffed out.

Saturday's poll will give everyone an answer.

It will tell us whether voters are willing to have him cut a swathe through the parliament with a band of largely unknown foot soldiers, or whether voters will return to their roots.

The latter is what Labor and the Liberals are hoping. Both parties have been running campaigns similar to those of the past, notwithstanding the threat posed by SA-BEST.

Labor has urged voters to look at the achievements of the past 16 years - the redeveloped Adelaide Oval, the new Royal Adelaide Hospital, public transport and road upgrades.

It's touted the party's efforts to combat energy woes, building the world's largest lithium-ion battery, supporting construction of the world's largest solar-thermal power plant and setting a goal of generating 75 per cent of the state's power from renewable sources by 2025.

But it also wants voters to believe there's much more to come. More trams, more road upgrades, better schools and hospitals, not to mention the jobs that those efforts bring.

The Liberals have, to some extent, played to their base, pinning their hopes on backing business to better foster economic growth and create jobs through tax breaks and other incentives.

But there are also other issues at play.

A recent redistribution of electoral boundaries, supposedly to make things fairer, has put the Liberals in a better position

SA's political landscape has been largely redrawn with Labor needing a swing towards the government just to win some seats it already holds.

SA-BEST aside, a number of independents could also play a huge role in who is the premier when the dust settles.

At least three - Troy Bell in Mt Gambier, Geoff Brock in Frome and Frances Bedford in Florey - are strongly favoured to be returned.

Add that to the Xenophon factor, and it raises questions of how power might be shared in the next government.

Marshall has ruled out any form of coalition with SA-BEST. But he'll no doubt welcome support on the floor from the likes of Bell, a former Liberal, and Brock, a one-time country mayor who was expected to support the Liberals after the last election.

Labor has been more open-minded about who it will deal with and it's shown in the past it can successfully broker arrangements with strange bedfellows to secure the government benches.

So, to use language similar to that of Mr Xenophon: SA has a Labor government that probably doesn't deserve to win but just might, and a Liberal opposition that really should win but possibly won't.

Australian Associated Press