That is subjective.
I grew up on Windows, from 3.1 to Windows 5.1 (XP), and I am very good at navigating those versions, but since I switched to Mac OS X and got to know Exposé, and since 2007 Spaces, I find it hard to navigate and control Windows (pre-Vista) as easily.
For instance, I work with Avid Media Composer, both on Mac OS X and Windows.
Using the same application on both platforms is really different sometimes, sometimes it takes me twice as long to accomplish the same task on a Windows box as it does on a Mac. But that is my subjective experience, as I have seen it the other way around.
And since the arrival of Windows 6 and 6.1, Windows is really foreign to me, and the colourfulness distracts more than it helps. It is just stupid eyecandy, that doesn't really help. With Mac OS X 10.5 and 10.6 Apple found a good way to mix colours and grey shades to not distract but support one's use of this tool (a computer is just another tool, though very versatile if one wants it to be), but 10.7 changed that to the worse. I guess Apple has only consumers in mind now, which don't mind the dumbed down version of Mac OS X, but there are still people left, who use a Mac for more than just Facebook and all the other clichés out there.
Anyway, in short, I find Mac OS X 10.6 more usable than Windows 6.1.