Marik's comment that professionals would vote for 10/2 and amateurs for 25/6 points to a way one can improve polls of this type: In setting up a poll, you have to state whether you mean 'harder to perform at concert standard', or whether you mean (basically) 'harder to sightread' or 'harder to play without having to practise a lot'.
It seems like Marik's observation, if correct, is largely due to the fact that professionals have to work on perfecting their pieces, whereas amateurs don't.
So it's no wonder that an amateur would consider 10-2 easier: 10-2 is far easier to sightread than 25/6, it's easier to bring 10/2 up to three-quarters of the required tempo and reasonably advanced amateurs can play short passages from it at full speed with minimal practise. If the same amateur starts work on 25/6, chances are that, in the time they've taken to get 10-2 up to 3/4 tempo, they still won't be able to play any given bar of 25/6 at even half tempo. At any rate, I think that describes my experience. I won't vote in the poll because I haven't got either piece up to concert standard.
Excellent post, Demented Cow!
There is one more reason. For amateur pianists double notes usually seem to be the most demanding and challenging type of technique. Usually, professionally trained pianists develope double notes from childhood and when the time comes to play 25/6 the main struggle is not with thirds, but with perfection of this etude for performing as a beautiful piece.
As you rightly noticed, it is much harder to perfect the 10/2 to high concert standards.
I attended many piano competitions, including several Rubinstein and Tchaikowski, where Chopin and/or Liszt etudes were part of the 1st round. I heard many folks there playing 10/2 and 25/6, where a lot of 25/6 were excellent. I can remember only one 10/2 you could say: "WOW!". It was Vladimir Ovchinnikov. It was beautiful--very musical, very quiet, very even, with no single note out of place. The chords in RH were perfect and did not loose one single note. LH gave beautifull support. The clarity was impecable, and pedaling was used only for giving right colors.
After the performance I asked him how did he practice it. The answer was about what I expected--slowly, for 5 years every day an hour. And this is the person, who had monstrous technical facilities, to start with.
Something to think about.