Aon has released its latest KiwiSaver report, which covers all multi-sector funds with more than $100 million under management.

Total FUM grew 4.4% to $31.6 billion. Generate led the growth with a 25.9% increase in FUM. BNZ, the last major bank to enter the KiwiSaver market, grew 8.4%.

Banks continued to dominate the KiwiSaver landscape, Aon said.

Between them, the big banks had 60% of the sector's assets and their FUM increased $940 million over the first three months of this year.

Over the past 12 months, Generate's conservative fund was the standout performer, with a 7.7% return.

"The fund appears to have benefited from a high exposure to domestic bonds and domestic shares and no exposure to overseas shares," the report said.

Global shares dragged down the returns of more aggressive funds. The growth manager median dropped to 0.8% in the first quarter.

Conservative funds were the best performers at the start of this year, returning a median 1.7%.

Over the past eight years, AMP was the worst performing fund in five of six categories, Aon said, and Aon topped five.

The report said riskier investments had paid off for KiwiSaver members.

"Over the long run investors have received some reward for taking additional risk. The median fund in both the balanced and growth categories returned 5.6% per annum over the last eight years compared with 4.6% for the median conservative fund and 2.5% for the median cash fund."

Only six out of 90 funds did not have positive returns over the last 12 months. They were mostly growth funds invested heavily in international equities. The NZ Funds Growth Fund was the worst performer, down 10.9%.