Mac OS X is going to be at least a tad bit more secure out of the box just by how it handles files. A normal user cannot write to the root directory, therefore, a virus would be theoretically limited to a user's home folder only, and not permitted to cause system-wide damage.
Apple is somewhat of the PC's personal beta tester though. I mean, PCs are just now BEGINNING to implement x86_64 into the Operating System. There was XP x64, but that was a corporate version. Apple has had 64-bit processors since the G5's introduction in 2003.
Even if that isn't quite right, the vast majority of PCs STILL don't have EFI. BIOS is obsolete, but normal vendors are dragging their feet, waiting to see how good it is with Apple's computers. EFI actually speeds up boot time by removing a step of booting, transferring to a software bootloader. under EFI, the Operating System's own loader (not the boot loader) is started directly.
Mac OS X also tends to be more integrated as well. In fact, you'll notice first thing you turn your Mac on, the operating system is so integrated with itself, there is a global menu-bar which handles operations throughout every application, no more hunting for menu bars on specific windows, just click a window (or its icon on the dock) and you'll have instant access to the menubar for that application.
Microsoft has yet to implement multiple desktops as a standard OS feature, and while it's definitely nothing new (Linux has had this for years), with the proper usage, it can speed up the workflow greatly.
Now I'll admit in this area that I don't know jack s*** about how well Windows 7 handles CPUs, GPUs, and multi-processor support, however I do know that Mac OS X 10.6 has certain new features, such as Grand Central Station, for better communication between the cores of a processor, OpenCL, for utilizing GPUs for processing power when they aren't doing anything better. According to Apple, modern graphics processors have the processing equivalent of a 10-year old supercomputer built right in. Mac OS X Snow Leopard will also include built-in Microsoft Exchange support, ironically a feature Windows users will have to pay extra for.
One also has to love the fact that Macs are actually cheaper in the long run. Windows PCs may be initially cheaper, however, with the cost of antivirus protection (sense the average user wouldn't know what the hell AVG was) plus operating system upgrades, you tend to come out with globs of money shelled out to Symantec and Microsoft over s*** that IMHO should have been implemented in the operating system itself. I know that Mac OS X doesn't have an antivirus built in, but you don't actually need one, at least not yet. Unless you spend more than 300 dollars on the "ultimate" version, you have to pay extra for DVD support, a feature standard in Leopard, and you don't have access to a media center, also a standard feature in Leopard. Oh, and did I mention that Leopard is only $129? Gee, $310 or $129? Mac OS X Leopard has the feature-equavlent of Windows Vista Ultimate, at the price of Windows Vista Home BASIC.
You also have to love the fact that there is only one version. It's like Steve Jobs once said:
We have a basic version, which is going to cost $129. We have a premium version, which is going to cost...$129. We have a business version, which is going to cost $129. We have an Enterprise version, which is going to cost...$129. And we have an Ultimate version, we're throwing EVERYTHING into it. It's $129. We think most people are going to buy the ultimate version.
There really isn't a need for all that s***. It was bad enough with Home and Professional, but at least those two terms were halfway understandable. The average user doesn't want all this s***.
And just to make Bill Gates look like a f***in hypocritical moron..here's a quote from Bill taken from an interview about Google's new operating system:
"The last time I checked you don't need two client operating systems," he said. "It's good to have one."
And thus I leave you at that. If you need anything else, don't hesitate to run around the streets naked begging for advice.