Spend 90% of your time learning C, because that is what the Arduino is programmed in.The other 10% of your time could be spent on the other languages.
Do you have any skills i programming? Bcause if you're just starting and don't know anything yet, you'd better start with the basis : algorithmy. It's not a language, just the "science" behind every language : how to structure your code, how the various conditionnal statements works, etc... If you can't understand the difference between a while and a if loop, start by this ^^
Of course, have stated that learning a little of more than one language is probably bad, I have to admit that I still feel a pull towards Python. I'm just worried that it's structure is so unique that it will slow me down and complicate obtaining a move advanced level of understanding when it comes to arduino code.