What’s it all mean?
Unfortunately, for those of us who just want a simple answer, the results of this testing indicates that one size doesn’t fit all. The Photoshop bicubic sharper algorithm seems to be better than anything for the particular down res-ing operation that I tested. Testing with a variety of resolution ratios might yield different results.
For up res-ing, it doesn’t seem to matter too much which of the tested algorithms you pick if you’re not making much of a change. For 150% or more increase in resolution, Perfect Resize is the probably safest choice.
For me, what algorithm I will be using is inextricably intertwined with workflow issues. More on that soon.