While I don't particularly like working with PHP I must say that if it's good enough for facebook, it's good enough for anything. If you're comfortable with it, I'd say you should just continue working with it.
If you're just starting, however, I'd recommend Python: it's easy to learn, powerful enough and there are thousands of tools and libraries for it.
It doesn't hurt to know at least a bit of javascript either, being the only language for front-end and all that.
As for the other two options in the question: