I tried a few and my conclusion is that none of them are very accurate or convenient to use. I can create the midi file faster by myself, either by playing it into a sequencer slowly one channel at a time (and then quantizing / correcting mistakes), or just hanging the notes on a staff using graphical music construction software.

PDFtoMusicPro can take .pdf files *that were originally created using music construction software*, and accurately convert them back to their source MIDI. But if you're talking about pure Optical Music Recognition from printed sheet music, I don't think the technology is there yet.