Both of them are powerful and can probably do as much as you need to do in digital scrapping.
Along with the regular Photoshop, they are the top 3 programs used in scrapping. This is good, since you will find more tutorials for these programs. I would say PSE it still more popular then PSP, so you will find more tuts for PSE then PSP.
Also, PSE has something called "actions" and they are pretty popular. PSP has the same thing called "scripts". Actions are very popular and can be found in many places, scripts are much less popular and hard to find, although that is increasing daily! Everything else can be used by either program.
Financially, PSP is MUCH cheaper. It is probably easier to learn out of the box, PSE has a larger learning curve. On the other hand, if you really enjoy scrapping, some day you may want to "graduate" to PS and you will have one foot in the door with PSE.