i have all 3 systems too.. each on different computers.
at work, all of our systems run linux (the best imo for reliability and large data work)
on my laptops, they all run vista (i have to buy new ones every year so it comes pre-installed)
at my home desktop i still have xp pro (older computer)
with linux i have alot less security threats, with vista security is good though it slows the computer when doing graphics, etc..., xp runs smooth- but, so much hidden spyware and viruses get passed even the best updated antivirus...
Mac's are rediculously overpriced. even my graphic design department switched away from mac products last year.