Well,
I was weaned on Microsoft but do not think it's the best. For the average person it's great, especially with XP.
Since I've found PhP and MySQL, the server side stuff has changed a bit for me. Both have advantages and disadvantages. This is like politics; are you right wing or left wing, simply pick your poison and go from there. I'm a-political, so I keep an open mind, especially when it comes to the ever growing computer technology. Look in all directions -
After installing medium sized gaming Windows NT/2000 based systems in casinos, Microsoft does put out some pretty solid server/client OS's. I've seen 10 POS's push a Windows 2000 server with a database by Mélange Inc pretty rigorously; taking thousands of customer's cash pretty effectively. So who's to say which is best, especially when clustering servers. It boils down to how they are set up.
For large scale systems, server arrays handle the juice, whether they are Linux or Windows based.
I say whatever works for each person or organization is fine.