So um... what do you want to do with the language? I work with VB.NET and Java professionally and Ruby, PHP, JavaScript, and the aforementioned languages regularly on the side. They all have areas where they excel. The language you pick depends a lot on what you want to do with it.
First of all, assuming you are a typical computer user and not interested in becoming a professional programmer, I see no reason to ever learn C. (That doesn't say anything about C# though.) I AM a professional programmer and I still don't know C.
If you want to program for the web, PHP is really the standard and a very good choice.
If you want to write typical computer programs (with a form and all), you probably want to go with a Microsoft language because the Microsoft Development Environment is by FAR the easiest tool for making forms/GUIs. I just wrapped up a fairly simple Java program at work and the code to make the form/GUI is something like 1500 lines. I use VB.NET, but C# is also a fine choice. Learning it will probably be more useful down the road as you learn other languages.
If you want to write small programs to accomplish simple tasks and don't care if they run from the command line, pick a modern scripting language like Python or Ruby. Ruby is my choice, but both are fine. Python is more popular. However, if you're just writing programs to meet your own needs, it doesn't matter which one you pick. I use Ruby frequently to do everything from generate passwords to use online to deal with large text files to move files around on my computer.
Java is somewhere in between. If your GUIs are going to be fairly simple, Java is fine for writing them, it just takes some getting used to. I haven't really found any tool for making GUIs that I really like, so I write them myself in Java. It's work, but there are actually some good features with Java GUIs. The language is somewhat simpler than the C languages (at least in my opinion) but not as simple as Basic. It also runs faster than Python and Ruby... at least generally. Java also has the benefit of being compatible with almost any type of computer. Also, of all languages, I think Java has the best documentation. The Sun website and the Java API can teach you how to do almost anything you could ever want to do with Java. Sun has numerous example programs and plenty of tutorials, and it's all well-organized in one place.
It's not a bad thing at all to pick up a little bit of a bunch of languages. I don't think I could even remember all the languages I've written at least SOMETHING in. I know I at least need to add C, C++, VB6, VBA, ASP, Perl, AutoHotkey, and Python to the languages I've mentioned already.
Really though, programming languages are tools. Like any tool, they have tasks which suit them. Picking a tool is not as important as picking a task. You will learn much more by actually writing a program you're interested in than by going through a tutorial anyway.
If you have any questions or want me to say more about anything I've said, just ask.