I go the other way around.
if you don't know how to program either, PIC Basic is going to be a lot easier to learn than the Arduino C style Language.
on the other hand, there is a bigger arduino userbase, and many more examples/libraries. -so even though it's probably technically harder, it's probably going to be easier to learn because there are greater resources.
the basic stamp is pretty much it's own thing, whilst the arduino already has a heap of different revisions etc.
what this means is that when you find that you don't have enough I/O or the chip isn't fast enough you're going to have to perhaps link multiple chips together using some kind of bus, whilst with the arduino, you can simply port your code as is from the arduino uno to the arduino mega...
All in all, different strokes for different folks, if you have a single application, and that's all you want, basic stamp is probably an easier language, and probably cheaper.
if you want to learn something new or you learn by example well and create lots of things, the the arduino is probably the better bet, if only for the bigger eco system.