Jay,
I agree with Frank and Daniel but also have some general comments. I use both products extensively but since this is a Mathematica forum I will only discuss Mathematica. They are good for different things. Mathematica has a "notebook" structure which is particularly good for maintaining a record of the derivation of your equations. It is also good for keeping a record of starting conditions, results, plots, data, and general comments and documentation. You can even paste images in the notebooks and interact with your notebook dynamically. I find the Mathematica notebooks replace paper so I do not lose or misplace my work. I hope this helps.
Regards