Id go to OSX myself, its rock solid (its Unix at the back end), and it is so secure its unbelievable.
But atm, Apple computers cost a bit too much and Risc isnt imho the way forward. I am glad they are now starting to take the Cisc route though.
Vista is a no-no for me though, I cant be bothered using an OS that requires a minimum of 1Ghz processor to run even half decently. To me, Microsoft have made Vista look fancy and have many new features, but have killed its efficieny in the process.
I want the 3Ghz in my laptop to be utilized mainly for running applications, not upto 50% just on the OS. And my media centre wouldnt like it, its a Pentium III 850Mhz, Microsoft rekon it would run Vista lol, but its cool, silent and XP does everything I want it to, with both efficiency and stability.