25 -1 is easy to learn, difficult to master. Far to many people miss the inner voicing and thus destroy the work. I would not say 10-3 is the easiest, in fact i would argue it is one of the hardest, as Chopin's own connection and emotion in this piece must be shown, and simply put, most pianists lack the musicality to really move an audience with this work. Also to play this etude as written (no pedal in main melodic line) is actually very difficult, combined with the very soft and gentle touch needed to voice 3 voices, at 3 different dynamics is no easy feat either.
I also disagree that 10-1 is easy. Horowitz refused to perform it in public due to its difficulty, and he mentioned in numerous interviews that he considered it the hardest of all the etudes. Ashkenazy is also documented as saying he never once gave a perfect performance of this etude.
I believe 10-9 is the easiest. 4 pages (2 of which repeat the other 2), a LH that never changes, a RH that's only change is using octaves not single notes. A very simple RH and very easy LH once the notes are learnt.