Bigger insurers tend to deliver more consistent returns, according to recent data, making them more likely to meet their projections of non-guaranteed bonuses.
But experts say it will get increasingly more important for consumers to do their homework, given changes in the industry.
One involves altering commission structures - financial advisers will get less of the commission in the first year after selling a policy.
This could put pressure on generating higher sales so consumers have to stay alert.
Research firm Wen Research's data and statistics from the Monetary Authority of Singapore show the returns of insurers' participating funds (par funds) over 10 years.
In terms of average returns, Great Eastern, AIA and Prudential were often in the top 25 per cent. These names are also among the biggest in the insurance sector here.
An industry veteran said: "How do you gauge who has a better probability to deliver better returns?
"There are a few measurements but an important one is the participating fund's performance. If the insurer's past returns are below what they project, the likelihood of not delivering it is high."
The returns affect bonuses of participating policies, also known as "with profits policies".
MoneySense, the national financial literacy programme, said participating policies are insurance plans that provide both guaranteed and non-guaranteed benefits.
The performance of the participating funds affects the non-guaranteed benefit amount, paid in the form of bonuses or cash dividends.
Two types of non-guaranteed bonuses are reversionary, paid annually, and terminal - which is an additional loyalty bonus.
Participating policies include endowment and whole life types.
MoneySense added: "How much you get in bonuses depends on factors like the participating fund's investment performance, the expenses incurred by the participating fund and actuarial assumptions."
However, it noted that bonuses may not necessarily track the rise and fall of investment markets, and insurers tend to smooth out bonuses over the years.
For instance, in 2009, "AXA adjusted downwards the reversionary bonuses of selected products in response to the severe economic downturn in 2008, as well as the lower expectation on future interest rates", said AXA Singapore chief financial officer Sean Yang.
Insurers that are doing well may not be generous with the bonus as distribution policies are not transparent, said a veteran. So even if some insurers are not frequently in the top quartile, they could be doing better with their bonuses.
Although Wen Research showed Tokio Marine Life Insurance Singapore was in the top quartile three times, the insurer has not cut its bonus payouts over the last 67 years.
NTUC Income, which made it to the top quartile once, said it maintained its annual and terminal bonuses over the last 10 years except for 2009 and 2015.
MoneySense said tracking participating policies requires looking at the participating fund's performance, its future outlook and the bonuses allocated - if any - to a person's policy for that year.
With a 55 per cent cap on first-year commission to be introduced, this means advisers will earn less in the first year of selling a policy.
They could be tempted to sell a more expensive product that is less suitable so consumers have to do their due diligence to prevent being locked in a long-term commitment they cannot afford.