Just for a bit of fun, I'll compare the two sets in difficulty one by one (disclaimer: this is personal opinion and whilst I have looked at over half of them in some detail, it is a long time since I have done serious practice on them - and some of the serious practice didn't work out very well, haha).
no 1: Alkan harder - the Liszt is quite straightforward.
no 2: Liszt harder - this is one of the more accessible Alkan etudes and the Liszt is full of difficulties.
no 3: Alkan harder.
no 4: Both difficult and I wouldn't want to offer an opinion.
no 5: Liszt is clearly harder.
no 6: Both are not that difficult but I'd say the Alkan is trickier - I had some troubles with the double notes.
no 7: The finale of the Alkan Symphonie is imo the hardest piece I have ever tried to play, so Alkan harder here.
no 8: The Alkan is harder, by dint of physical effort required if nothing else. Unless you're going to try to play the Liszt like Berman or Villa.
no 9: Pass. I don't feel able to comment.
no 10: Alkan harder, though I think it's not quite as hard as its reputation.
no 11: Alkan significantly harder - the Liszt is comparatively accessible and in this case the Alkan looks reasonable on paper, but a few hours looking at it and you will change your mind.
no 12: They are both extremely difficult but in very different ways. No comment.
Anyway that's just my opinion for what it's worth