Disagree If you mean in terms of stability. Windows 8 & the Windows 8.1 preview were extremely stable, I used it as primary OS for a while.
I concur, I ran the Consumer Preview and have the RTM now on my main machine at work and its stable, no problems with. With the release of Windows 7 beta, Microsoft started really producing very stable releases of Windows from the get go.
On the other side, OS X seems to have always been a buggy product, in beta and GM releases. The last two releases have pretty much suggested it has gotten even worst. The last stable release which I see a lot of people still run is 10.6, prior to that it was 10.4 then 10.3.