SharpEye

• Very limited in options/functionality.
• Cannot read PDFs or JPGs.
• UI to see and check results is inadequate (renders results separately from source image, and without wrapping).

SmartScore included in Finale

• Cannot even open images, works from scanner only.

SmartScore X2 Pro, Standalone

• Not a great UI at all, but maybe, just maybe not quite as bad as some of the other stuff.
• Result rendering, when I got it too work, was good (original and results separately, but scrolling synced).
• Cannot read PDFs or JPGs. Crashes on BMPs. Does not properly read TIFFs (it kept loading only parts of them, but strangely skewed). Originally I had managed to load a file, but then couldn’t reproduce it later.

capella scan 8

• UI: It’s just a regular Windows app with a menu and toolbars. That puts it heaps and bounds above anything else here.
• Someone actually bothered to support such cutting edge formats like PDF and JPG. Very good.
• Overlays the detected elements with the original image, making it very easy to see what was missed. Perfect.

ForteScan

• Since the manufacturer also sells SharpEye, at a higher price point, I didn’t look at it.

PhotoScore Ultimate

• I see an ok UI in principle, but it’s almost unusable in OS X. Don’t think about minimizing the app.
• Cannot open JPGs (but does support PDF!).
• UI to check the output: There is apparently some overlay going on, but I found it utterly unhelpful.

It was such a paint fighting through the UI and format issues that I didn’t bother to look closer at comparing the actual results. Sometimes one seemed to handle something better than sone other. They all generally seem to work, but rarely without mistakes, even for seemingly pretty good scans of simple music.

Speaking of terrible UIs, if you want something that is pleasing on the eye, definitely use Sibelius over Finale.

Playing from digitized sheet music

• forScore is a good app, but how well it works depends on the sheet. Sometimes the notes are too small. Manually cutting away whitespace at the margins sometimes helps, but is a huge PIA. MusicXML is needed here.
• The only MusicXML iPad app seems to be SeeScore, but is incredibly limited, awkward to use and buggy.
• A bigger screen would help, but there doesn’t seem to be any forScore-like performance program for OS X, apart from the unusable MusicReader.

Update August 2014:

There is also Audiveris, which is used by the MuseScore PDF Import.