Mac, and the reasons that I do is because I demand reliabilty and a platform that runs flawlessly.
I do a lot of photo editing and well, yes photoshop runs in PC, I find it runs so much better in my mac.
Also the hardware API is written so much better so yes, it costs more. My 2 year old macbook pro is running just as fast as it was the day I bought it. Did it cost more? Yes, but I know it will work when I turn it on and not crash when I'm doing a batch photo move and edit and resize of 400 pictures. I know it won't crash on me. That alone is worth the cost.