I first encountered Idil Birets's recordings of Liszt's transcriptions of Beethoven symphonies when they first appears on LP under the EMI label. But I don't think that is the only reason why I rate her recordings above all others.
The performance of the first ninth symphony is pure magic. Of course much credit must go to the genius of Liszt in scaling down this momentous work for solo piano, and part of that skill is as much in what he leaves out as what he puts in. But Biret brings something special to this work. The slow movement which could so easily without the colour of the orchestra become monotonous is anything but, such that every time I hear it I do not want it to end.
And when the first soloist comes in in the final movement, and the melody is played with just single notes, Biret succeeds in making the piano sing.
In addition to Biret's recordings I have all of Cyprien Katsaris's on Teldec and most of Konstantin Scherbakov's on Naxus. Neither of these approaches Biret for the subtly and the beauty of the playing, or the recording sound. I would also choose this solo transcription over Liszt's transcription of the Ninth for two pianos, where for the most part there just seems to be just too much piano, certainly this is the case when comparing it with the recording by Fabio and Sandro Gemmiti.