Ask the two candidates facing off in Sengkang West whether either of them has the advantage and both will answer: They don't know.

The candidates - People's Action Party's Lam Pin Min and Workers' Party's Koh Choong Yong - are not just being politically correct.

Nearly 40 per cent of the 30,119 voters in the single-member constituency going to the polls on Sept 11 did not vote in the ward in the last round, which means there is a big mystery over where these voters lean.

Since 2011, 15 Build-to-Order (BTO) developments with about 10,500 flats in all have been completed in Sengkang West. Part of the ward, the area between Jalan Kayu and Fernvale Road, was redrawn into Ang Mo Kio GRC. Some 26,882 voted in the last round.

Speaking to The Straits Times, Mr Koh said the 2011 election results - when Dr Lam won 58.1 per cent against his 41.9 per cent - cannot be projected onto the latest contest.

Dr Lam said voters will have different considerations at the polls: "To the older Singaporeans who have seen Singapore transformed from Third World to First World, they will appreciate the journey the Government has walked with them and the undeniable fact that it has delivered on its promises.

"For the younger voters, I believe the aspirational concerns will weigh more heavily with them."

What is clear is that both men are offering very different choices to the voters.

Dr Lam, who was first elected in 2006, has been pounding the ground, improving infrastructure and rolling out new amenities in the young estate.

Under Dr Lam's watch, new facilities such as Seletar Mall, Anchorvale Community Centre and Sengkang Sports and Recreation Centre have been built. Dr Lam said he "understands the needs of residents much better".

The Minister of State for Health has also promised a dual-carriage LRT and better buses by next year. On the horizon are a jumbo childcare centre in Fernvale Lea and an integrated community facility with food options.

But being the incumbent also has its downsides. One issue that Dr Lam has had to deal with was the columbarium saga which had generated some unhappiness among new residents. Last December, news that a commercial columbarium was being planned for a plot of land earmarked for a temple, near BTO homes in Fernvale Lea, met with protests from residents.

Although Dr Lam acknowledged that the columbarium issue could affect voters to a certain extent, he said the matter has been largely resolved.

He added that residents have not raised the issue to him during his house visits.

"If elected, I will continue to work to make Sengkang West an even more endearing home for all of us," said Dr Lam.

For Mr Koh, his platform is straightforward: Vote him in if residents want an alternative voice in Parliament to weigh in on national issues, he said.

Mr Koh, who worked as a legislative assistant in WP's Aljunied GRC and Hougang SMC post-GE2011, said voting opposition makes for a more responsive government, and he is encouraging voters to think beyond municipal amenities in the short term.

If elected, he aims to speak up on issues he believes strongly in, such as education, job security and retirement adequacy, which he feels resonate with voters.

He said: "We give people a choice... There are residents who come up to me and say thank you very much for standing so that we have a choice between you and the PAP."

Sengkang West residents said they appreciate Dr Lam's efforts although many also said they would like to see a stronger opposition.

During Dr Lam's house visits last Saturday, retiree Robert Ang, 62, clasped his hands tightly, urging him to go all out to capture the hearts and minds of the young.

Mr Ang said: "Most of us older people will vote for the PAP because they have good policies and we want a good government for future generations."

Housewife Nina Adam, 36, said: "Dr Lam has been doing well but we are also hoping to have someone who can help us out on national policies to address issues such as the rising cost of living."

Addressing younger voters, Dr Lam said the "Government has heard them".

"We are moving to meet their aspirations. However, some things do take time to realise. What the younger voters can be assured of, if they vote for the PAP, is that we have delivered on our promises and will continue to work with you, for you, for Singapore," he said, invoking the party's slogan.

But even as the campaign trail heats up, the rivals hope to keep this a clean fight.

Said Mr Koh: "You may have different views on policies, but at the end of the day, we're all trying to make Singapore better."