Fund manager Mercer's second quarterly KiwiSaver Survey shows growth funds performed best in the period, producing a median return of 10.8 per cent.
But if returns are compared over the two years since KiwiSaver started, the default funds have been the best performers - with a median annual return of3.9 per cent, compared with -8.1 per cent for growth funds.
Martin Lewington, head of Mercer New Zealand, said in the past six months balanced and growth funds had pegged back about half the losses they suffered during the global financial crisis.
"This result is in stark contrast to the previous 12 months in which only conservative funds, on average, provided a positive return for KiwiSaver investors."
Mercer's data shows that if an investor had put $100 in a KiwiSaver growth fund in September 2007 it would now be worth $85.
The same amount invested in a balanced fund would be worth $95.
Only those who put their money in a conservative fund would have seen growth in their investment, at $107.
Mercer surveys 61 funds each quarter.
Of those surveyed, the best performing growth fund in the three months to September was Fisher Funds Growth Fund, which experienced 15.2 per cent growth.
It was also the best performer in the past 12 months, at 20.3 per cent growth.
Of the default funds, Mercer's KiwiSaver Conservative Fund came out on top, growing 6.5 per cent in the quarter and 3.2 per cent in the year.
The best performing conservative fund over the quarter was the Mercer Conservative Fund with 7.3 per cent growth.
However, the AXA Conservative Fund did best over the year at 8.5 per cent growth.
In the balanced category, Mercer's Active Balanced Fund did best with 10.9 per cent growth in the three-month period, while the Mercer Moderate fund did best over the year at 7.4 per cent growth.
Lewington said KiwiSaver funds under management were increasing at an unprecedented rate, with the six default funds growing at an impressive 36 per cent in the September quarter.
As at September 30, 1.19 million New Zealanders had joined KiwiSaver, with $4.25 billion transferred to KiwiSaver providers.
