Start with C/C++ class of the languages.
Java/Ruby are (in my opinion, easier - but it will be hard to learn more basic language after Java - since so much is hidden from you by the language).
If I had to start over again (im not a pentester, im a programmer) I would do C/C++ and perl at the same time (perl just for fun -when you need a brake from C).
C/C++ are close to the source (source = less of abstraction layer) enough to actually learn about sockets and pointers, memory allocation etc. After that all others are easy (opinion again).