Simply put, the best!
I admit its been a while since I researched other flashcards apps in the App Store. But last time I looked there was nothing even close to AnkiMobile.
It seems the goal of the developer is to give you the best environment for learning and retaining things as opposed to a "bells and whistles" approach some others seem to take.
I have 70,000+ cards in my deck and AnkiMobile sorts through that huge sea and and brings up the relevant cards according to its spaced repetition algorithm with lightning quickness. Its amazing!
John_63f about
AnkiMobile Flashcards, v2.0.19