"matplotlib seems a good contender to me'

I've waxed lyrical about Python all over this thread, but here you have to give the medal to R. Matplotlib is one of my least favourite libraries to use, been doing it for almost 2 years, and I still spend half my time buried in the documentation trying to figure out how I'm supposed to move the legend slightly to the right or whatever.

ggplot probably has slightly less flexibility overall (mpl is monolithic), but for just doing easy things that you need 99% of the time, ggplot is king.