I've worked at both MS and Apple during my career. And I hate to deflate any fanbois' expectations. But, majority of employees from both companies not only love both operating systems but use them both as well.
There is no "best". Just "best for me". I have both in my home. But, I'm also not limited by a budget that only allows me to own a single computer.
But DESIGNERS use Apple stuff - WORKERS use Microsoft. There is some overlap between these users, some prefer applications which are windows-only, and if this happens, they do Boot Camp.
The Best Windows XP/Vista and 7 machine I have ever used was a macbook Pro - I was so amazed that it has become one of my goals to get one somehow.
One thing I have seen though - Apple Employees respect Microsoft stuff - And Use it to make their Apple stuff better. If Microsoft does not do the inverse, they are stewpid.
I work for a software company. We have offices in Australia, the UK and the US. A handful of developers started requesting MacBook pro's instead of their Windows based Dell's at the office because they used MacBook Pros at home and really loved them. So, we allowed a few people to get MacBook Pro's, and then all of a sudden we had requests coming in out of the woodwork from people who also wanted a MacBook Pro. In addition, in our UK office we acquired another company that are all on MacBook Pros. Well these guys won't give up their MacBook Pros either, they say it's what they use at home and they love them..it's what they want to use.
These are very technical and savvy people. These aren't employees who simply don't know better and are following the rest of the sheep in the herd. They are using Mac's because it's what they want to use, it's what they have asked for and it's what makes them happiest.
As a company, we have found it's easier to keep them happy then force them into a Windows machine. We are following the trend of less corporate controlled IT and far more consumerism and consumer based devices.