Every company believes that their product is the best. Allot of it is opinion. I can tell you personally, I have a Windows 7 system that I built and I only use it for Gaming a and a few other things that require Windows. So it is great for me on that. OSX I use for everything else. I am a security engineer by trade so it basically gave me the stability of unix, the compatibility with allot of open source applications either through darwin ports or through my own code compilation so I had access to tons of network and security tools and I have a fantastic multitasking gui interface that allowed me to yes productivity applications like office. Can i say one is better than the other..... absolutely, but it depends on the use. Can anyone say one is more advanced than the other...no because I did not write the code to tell you for a fact. I can tell you that based on my use, it is not that it is massively better than Windows but what it does do better than windows is significant. You see, Apple is a engineering company, they pay attention to the little stuff and there are tons of little things that they nail.
I can tell you for a fact, the system does not slow down over time, does not slow down when loaded with applications, manages the disk much better, has better backup features, does not has the number of viruses available, is stable, has a much more efficient IP stack, has better built in parental control options, has better multitasking ability, has built in data encryption features, has better connection sharing features, has better system search capability, has a better filesystem, has ssh, scp, tcpdump built in. Closer adherence to RFC's (really due to it's unix underpinnings), handles multi threaded applications much better, much better memory management. I should go ahead and stop.
This basically again based on how I use the OS though. Someone else that is a more traditional user type might have less to compare against.