It's not even goroutines. Its the scheduler. I am continuously impressed by the amount of quasi-generic performance they can get out of something so simple. You can understand the entirety of the golang scheduler in minutes, and it works out of the box for most of my golang use cases.

That said, the JVM scheduling is pluggable, so I have options for a much bigger variety of use cases. With go if the default scheduler doesn't do what I want, I'm stuck.