I would generally agree with Rick's assessment that the Sibley app is
my first and last stop for field guide apps. With that said I will add
the caveat that there is supposed to be a new version of the app
incorporating the improved artwork, maps, and taxonomic changes of the
2nd edition of the Sibley books. It's unclear whether the second
edition app will be a free upgrade or if new users will have to pay
again, so many folks have been waiting to spend the money until that's
announced.

Unfortunately, the app is almost four years overdue (originally it was
supposed to coincide with the book release in early 2014) with no
known release date.

Josh Adams
Cathcart, WA