OSX is better because it doesn't feel too different from Linux (aside from setting docker machine ENV variables). Still virtualized so you take a performance hit.
The beta announced a few days back by Docker uses HyperV to boot a Linux kernel to run Linux Docker.
The preview announced around a year ago by Microsoft and Docker is a native Windows implementation of Docker, running on the next Windows OS.
[later]
But...
This new layer should let you run most Linux containers straight on top of the next Windows.
Interesting...
I wonder how they will make Ubuntu happen on Windows. Reading some of the comments, some speculate a subsystem, while others suggest an interoperable interface.
Edit: reading bitcrazed's comments it looks like it will be implemented a la WINE. No need to recompile binaries made for Linux x86; you'll be able to run apt packages from Ubuntu out of the box.