In a statement, the Australian Competition and Consumer Commission said Optus had overtaken TPG which had led the previous five reports.
The latest ACCC Measuring Broadband Australia report showed that in August, all retail service providers averaged between 76% and 87% of their plan download speeds.
It said Exetel, Telstra and Optus improved speed test performance while the other RSPs saw a slight decrease in download speeds compared to the previous quarter.
“This shows how RSP performances can vary, and why it pays for consumers to do their research. We encourage consumers to compare the busy hour speed claims made by RSPs with their real-world performance, as set out in the Measuring Broadband Australia results, especially if they are paying more in the expectation of faster broadband speeds.”
The report also found that hybrid fibre coaxial connections experienced the highest average daily outage rate, recording one every two to three days. HFC connections also recorded long outages of more than three minutes more often than other technologies.
The outages could be reduced when NBN services were not being added at significant volume, and legacy services no longer occupied some of the HFC network capacity.
Consumers on fibre to the node connections experienced slightly fewer outages, although most lasted for more than three minutes.
Fibre to the premises connections generally recorded few outages of more than 30 seconds, and most lasted for less than three minutes.
Reacting to the ACCC announcement, Dennis Wong, managing director of Optus Networks, said: "We are thrilled that Optus has the fastest NBN peak evening speeds independently tested by the ACCC.
"The results reflect the considerable investment we’ve made in our network to improve our customers’ experience and ensure they consistently achieve a high level of performance.
"The ACCC report provides more positive news for Optus following the launch of our truly unique 5G network this week, which promises to deliver customers a game-changing, world-leading experience on their 5G home and 5G mobile devices."