Un sospiro was the first piece of Liszt that I played. It was very comfortable to play; the only parts I struggled with were the cadenzas because I hadn't played any Liszt cadenzas beforehand. I thought it was very fun to learn and perform this piece --> everyone loves it!
I voted for Chasse-Neige and La Campanella, because tremolos are difficult to control. La Campanella doesnt look that bad, but then I imagine trying to look confident while performing it, and then I feel weak.
Do you have a teacher? Your teacher would know your individual strengths and weaknesses and would be able to help you choose one.
Chasse-Neige is really hard and so is Campanella, but if you put your weight into the keys and do rotations, even 45 trills aren't so bad. La Campanella, I read, is the least valuable, musically, of the paganini Etudes.
I think Appassionata is an incredible piece, but to do it justice would be, I think, harder than most of the others. The same would go for the Op. 25 No. 12.
I believe Un Sospiro fits well under the fingers.
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For us musicians, the music of Beethoven is the pillar of fire and cloud of mist which guided the Israelites through the desert. (Roughly quoted, Franz Liszt.)