It is close to...if not...impossible to erase a HD.
Given enough time/effort/money....data can be recovered.
Of the methods you mentioned.
They may give a data recovery house a little heartburn....but just a minor speed bump.
I know the textbook explanation difference between these two, but am interested in real world experiences you may have had in the efficacy of these two algorithms for preventing restoration of files that were shredded from:
1. Standard hard drive - internal or external
2. Flash memory USB key