I use unrealBook. I have not (recently) compared with others, but I have taken advantage of a lot of the features of unrealBook: the "keywords" database (metadata) so I can search for songs by specific artist, year it came out, creator of song, genre, whatever else I put into my keywoards (metatdata). Took a while to do, but I use that feature a lot.

I also use Set Lists a lot; MIDI (sending MIDI to my Tyros5 to recall Registrations for songs). unrealBook seems relatively easy, and natural, since it was created by a musician. I have also got to know the developer pretty well (Via emails about features etc.)

It could be that other apps can do all these things, but I've kind of "grown into" using unrealBook so it's hard to consider switching after I've put a lot of work into setting up unreakBook and my PDF (songs) so they work they way I want them to ...

Jim