Some would say Python or Ruby. I suggest both. Once you learn one, it's very easy to pick up the other. As much as their similar, their library support and tools make them useful for different purposes as much as the same purposes. To go into a little detail, if you're building a website with some offline or non-web aspects, go with Python. If what you want to build is entirely on the web, go with Ruby on Rails / Sinatra. With these skills, you can build awesome web apps and tap into the huge library support of Python for non-web related issues.
Finally, you just have to learn Javascript if you want to dive into web. Start with pure Javascript, some jQuery and pick a library (Backbone, Ember etc...) and learn it.
You are almost right. There is one language that is the best, though it's so young it doesn't stand out yet. This might be the only time in history people still have the chance to contribute to the best language.
That is, Arc: http://arclanguage.org
Anyway I would recommend just trying every language, so you can select the most suitable one depending on the project.
The other languages and frameworks are neat, but I can't help thinking the above will be around long after the current and next trends die.
Though I do prefer python.
There are many tutorials and screencasts of the various frameworks for the different languages.
Main thing is to just try them all out and see which clicks for you.
Enjoy.
Edit: And Javascript!