Worst MS product: Definately Windows ME.

Best product: I gotta say Flight Simulator. I've played that game since it was played on a black/green screen. And even then it kicked (I need to watch my language). However, a close runner-up is the newly aquired foldershare. What a brilliant concept.

Highest quality product:Since I'm a professionel developer, Visual Studio and the .NET platform immidiatley comes to mind. But the office products, especially excel and word, are also very good candidates.