My learning style is simple.
First day, for the first time I sightread entire piece, then play it twice or three times more from the beginning to the end, but already with stops, paying attention to the hard spots.
Second day I do the same, carefully analyzing whole logic of the piece, its entire structure and any details I can grasp, hands separately if needed.
Third day I sightread it through again, and then start memorizing. I would not go to the second page until I know the first, and so on for about 3-4 hours.
Next day I start from the point I left the last day and do the same (I don't get back to what I have learned yesterday, yet).
After I got to the end of the piece, certainly I've already forgot what was in the beginning, so I run through the piece again, exactly the same way.
The third time is the last one--I know the piece from memory, and that's where the whole work on the piece starts.
I don't have an exceptional memory and I am pretty lazy, so I don't learn very fast, but usually this way it takes me about a week at the most, to learn a very hard and lengthy piece (something like Liszt Sonata, for example).
The longest I remember was Rachmaninov 3rd Concerto 2nd and 3rd movements. It took me exactly two weeks to bring it to the first lesson playing from memory.
I was practicing 9 hours a day every day.

The quickest I remember was before a competition, when my teacher called me at 2 PM, asking to bring a complete Schumann Concerto TOMORROW. Needless to say, I never saw even one note of it before.
And you know, in Russia if the teacher tells you to bring a piece, it means it should be from memory, in tempo, with teacher's accompaniment, and so on.
I remember getting a full bag of sandwiches and practicing from 3PM till 6AM straight. And what do you think, next day at 4pm--my lesson time--I was playing entire Schumann concerto from memory.
I stil remember after the lesson my teacher told me: "Good for you, but you know... on a second thought the Tchaikowsky 1st probably would be a better fit for you"
Since then I never even opened Schumann Concerto score
