Relatively easy to master. Documentation and support is excellent. 2D and 3D graphics facilities. Most standard file formats are supported. The package includes image processing utilities.
Plots are journal quality with full postscript support.
Text labels can be easily inserted for point identification. It also does 3D graphing. I use DeltaGraph quite a bit, but I don't have much experience with these particular features. I'll refer you directly to DeltaPoint for your specific questions. Regarding your request for information on nonlinear fitting and graphing software.