Both companies copy from all over the place as well as provide their own innovations. The question is: which one is better for you and the ways you need to use them and their peripherals ?
If I were to compare Windows Vista to OS X Leopard, both of which I consider less than perfect from both companies, I would still pick Apple. Vista could do a lot but from the point of a techie who has to fix this stuff, Vista may have been too unwieldy and prone to crashing. I don't see any one part of Vista not well designed though. On the other hand, while OS X has been great in its long history, Leopard's stubborness in not talking nicely to a Windows network could be a headache for Windows admins. Our school, which trains new students and veteran techies alike, just did away with the Macs on the Windows Server networks. I don't quite know what the issue was, but Snow Leopard seems to have fixed any of those issues lost in translation. The docks of both the OS X versions could be a little cleaner as to showing what is open or not. I would like Lion to go back to a black arrow icon as seen in Tiger to show what's open or not, especially on all those Macs with shiny screens.
But today, with what appears to be a very strong and stable OS X version in Snow Leopard and a very solid rendition of Windows in version 7, the OS which is easier to use is probably the one which the computer user is more used to.
The public is very lucky right now in having the choice between Snow Leopard and Windows 7. While I like OS X, I will say that the most improved OS over the years has been Windows. I think in the past they had a lot of catching up to do, and they have grown at a faster pace (in user friendliness) than OS X. But OS X started as a pretty easy to use OS from the beginning.
In the end, it's personal choice, and not one OS being far superior to the other.