Depends on what you're doing. In my research the moment I'm working on difficult to access data or with new techniques, Python becomes the better tool immediate

Depends on what you're doing. In my research the moment I'm working on difficult to access data or with new techniques, Python becomes the better tool immediately. R is absolutely beautiful for manipulating small data sets. It's the only reasonable way to plot things (with d3/protovis coming in a distant second) and it's supercharged by Hadley Wickham's work. It's also totally crippled for "general purpose" programming and turns to C every time you need more speed.