There are lots of web designing software available in market today.
According to me the best web design tools are all Adobe products, such as...
Adobe Dreamweaver, Adobe Photoshop, Adobe Flash, Adobe Creative Suite etc..
I think PHP, Dreamweaver are the best web designing software as these both softwares are used by all web designers. Also these are fully upgraded software with all additions features and applications.
The best web design software for you may depend on many factors. You will need to determine how advanced it needs to be, as well as how easy to use. I think, the best web designing software are HTML, Dreamweaver, photoshop, PHP, .NET,
DreamWeaver is really nice but it has an advanced learning curve. Publisher is easy to use and compresses photo's to save space. CoffeeCup is good if your going for a free solution. It really depends on what your site is about and what kind of scripting you are going to do with it. I would get a trail of each and see what one works for you the best.