TE 10 is more difficult.
Why? Because La Campanella is much simpler as a piece.
I played both and can comfortably say that this etude challenges not only the techniques and the jumps, but also fluidity. Playing the left and right hand is the easiest part, but the LH has to be in a constant rhythm. This is not easy to do when there are jumps spanning 2 octaves.
There are also polyrhythms too to worry about. There are 3 against 2, 3 against 4, 4 against 3, 5 against 3, and more. The technique is much more varied, meaning you must be fluent in multiple skill fields.
La Campanella doesn't have any of this, sure, it has jumps, octaves, and trills, but basically, all Liszt's pieces have that. It is a great show piece, and it's not easy by any standards, but you just can't compare them too. The technique improves with practice, but for TE 10, if you don't know what you are doing, you will never be able to get it.
I heard a lot of people suggesting about the octaves in TE 10 and the stretta. The STRETTA IS NOT THE HARDEST PART. It looks impressive, and it CERTAINLY IS HARD, but it is one of the easier parts IMO in this piece. There are so many other pitfals to worry about, and not to mention La Campanella has that too, and it's 1000x easier and simpler. The hardest parts in La Campanella is the 4-3-2 repetition near the middle, for that practice is straight forward. FOr Trascendental Etude No. 10 simple practice just doesn't cut it.