Largely for historical reasons, I mostly use R. It requires a lot of care & feeding, but rewards you with a lot of control. A colleague uses MatPlotLib under

Largely for historical reasons, I mostly use R. It requires a lot of care & feeding, but rewards you with a lot of control. A colleague uses MatPlotLib under Python. He makes nice-looking plots with it, and when I watch him driving it, I feel like I could learn to work with it pretty easily. The only reason I haven't given it a real try is the cost of setting up the larger framework I would want to use to generate the points I plot. I used gnuplot for a project. It's conceptually easy to work with, but the inconsistent looks between different output formats (e.g., PNG vs SVG) made me choose it simply because scripting it from the command line was easy. Another gripe I had was that, given a file with multiple columns of data to plot, it has to parse the file once for every curve it puts in the plot. Finally, I found gnuplot wasn't very smart about how it chose points when plotting expressions (e.g., telling it to plot "sin(x)" rather than passing it points on a sine curve). Re guides, I liked William Cleveland's "Elements of Graphing Data". However, I'm not widely-read on this subject, so this is kind of one point in the noise.