Econometrics, Bioinformatics, Game Theory. Python or R?
hs: my friend told me that econometrics is his hardest phd qual.  iirc he mentioned statistics, time series, and stochastics (very heavy maths) ... to me those seem to be best handled with statistical package like Rmy bio friend told me about string matching, she used perl.  i'm not sure if R can do pcre regex pattern matching.so yeah, you may end up using R and python.  if i have to decide, i'll use pyton, because it's more flexible