I have to add a warning here: if you really want to compare different apps to focus stack several images, you need to be fair with the them (the apps).
Focus stacking is a really difficult process that involves among many other things making decisions about which regions are focused and which not, and then usually resize (and sometimes rotate) images to align them with each other.
Currently there’s no program capable of stacking raw images. That’s a fact. The only claim they honestly can do is that they are able to take a raw image as an input and then process it before the stacking process. So, who is better to decide the best raw processing for an image? A program with a standard, canned pipeline, or the one who has shot the raw images?
And if you wish to have the closest possible to a raw image, then process it an export to tiff, as a bare minimum.
But among the most important things when shooting images to focus stack them is to overlap the focused strips between adjacent images:
Same as @paperdigits has remarked, I have pointed to one area (among a few others) that has never been focused in any image. That’s called «banding», and happens when you focus too far away from the last image shot, and then there’s an area (a band) that is never properly focused.
This is important because different algorithms (programs) deal with banding quite differently from one another, even leading them to really weird artifacts (I have compared quite a few programs). So again, to compare programs, you better make sure that your images do overlap.
There are other artifacts here, like chromatic aberrations, and halos, that should be avoided when comparing programs. And about the halos, if you’re talking about the dark halo above the coin, maybe the problem lies in the lossy image compression (they are jpegs) and the fact that the top of the coin has never been shot focused, so the algorithms do their best guessing that part.
If you are a casual focus stacker, then any all automated stacking software is good, but on the other hand, if you really are into focus stacking and want the best results, then you absolutely have to visit www.photomacrography.net - Index page