Which ever os you use, there are always goods and cons.
Windows is crappy in my opinion, but yet, it's everywhere and compatible with almost everything.
Linux isn't as popular and you can have lot's of problems configuring things on it. It's more personalisable than windows and is widly used to hack but can as easaly be hacked as windows.
Knoppix (a GNU/Linux distribution that boots and runs from a cd) is an other option I really like to have 2 os on the same system at a time. I use it more and more and will never go back to only one os.
Mac... well mac is a mac, you like it or hate it. I don't like it, never will, and it isn't as secure as people think it to be. It is very good for graphic designs and is widly used in marketting technologies.
The problem with people is they tend to get caught up in many many goof and crappy add on programs that will supposively protect and all. If I had it my way, every internet connection would have a physical firewall on it and an integrated anti-virus to go with it. Would slow down the virus spreading.