[Nyororin]

The best way is most likely a combination of all of those, really. And it also depends very heavily on your learning style and your determination.
Wait, D and E probably aren`t going to get you far at all.

I personally went with G. :P Leapt from greetings and bodily function (I`m hungry, I`m thirsty, I`m sleepy, where is the toilet?) to functional fluency in less than 6 months. (Please don`t mistake that for true fluency - that took a bit longer.)