I think you should use what makes you more comfortable. I have never professionally worked with Java so I'm going to jump to the other two.
I think either choice, be it Python or Ruby, it's not going to disappoint you. I use them every day and sometimes I even get syntax errors because I'm writing Ruby in a Python file or vice versa.
Although I have been using Ruby for quite a while I still think I am more proficient with Python.
For web development you can't go wrong either way. I would start with the most used frameworks for each language: Rails for Ruby and Django for Python.
There are so many resources you will definitely feel overwhelmed :-)
If you have specific questions ask away!
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