languages for bioinformatics

So my bioinformatician friends tell me that the two main computer languages they learn are Python and R.  If you are doing bioinformatics, which language do you use most and why?  For those of you who wish to learn, here are links for courses on  

1. Python
2. R





(The missing link for Learn the R statistical programming language has been fixed now)

Quantitative Biology Workshop starts on March 29, 2016

https://www.edx.org/course/quantitative-biology-workshop-mitx-7-qbwx-1