TL;DR
The -standalone- Think Broadband Speed Test is the best IPv6 speed test.
What is the best IPv6 speed test?
In a previous study we investigated whether there are differences when testing internet speed via IPv4 or via IPv6.
It was concluded that lower speeds were measured earlier based on IPv6 than based on IPv4.
However, the differences are so small that accuracy is by far the most important characteristic of an IPv6 speed test.
Over time, we have discovered several speed tests that claim to be able to test internet speed over IPv6.
Of these speed tests, only the standalone version of the Think Broadband Speed Test and MySpeedMeter received 4 stars based on our standardized speed test test.
That's why we decided to compare Think Broadband (standalone) with MySpeedMeter. The conclusion is clear. The -standalone- version of the Think Broadband speed test is the best IPv6 speed test because the usability is much better.