This question stumped me for a long time. For years, I built all my web sites by hand. I wrote HTML and CSS in a text editor named `vi`. This is not what I would recommend, but it worked for me. Unfortunately, that left me without a good solution to recommend!
In the last year, I've been working with WordPress and Drupal. I've also experimented with Joomla and TikiWiki.
These are all CMS's (Content Management Systems) that people use to build web sites. They differ a bit from HTML design tools like DreamWeaver or HomeSite.
The real answer to this question depends upon what type of web site you want to build.
For a first web site, the easiest answer is WordPress. WordPress is free and it is very easy to use.
You can download free WordPress themes or you can buy some incredibly fantastic WordPress themes for under $300. You can hire WordPress theme designers at very low rates who can customize the look and feel to just exactly what you want.
WordPress makes it easy to focus on content instead of on the technical side of site building.
There are thousands of plugins to WordPress which extend it in all sorts of directions. You can make a lot of different types of sites with WordPress.
But, you can't build everything out of WordPress. This forum, for example, is built using vBulletin. vBulletin is the best forum software available. I would not recommend using WordPress to build a site that was going to be a web forum.
So really, it all boils down to requirements -- although WordPress is a good "default" answer.