some candidates -
michelangeli
hamelin
yundi li
cziffra
pollini(....in the studio at least)
so...
Michelangeli....I have found two mistakes or smudges in his recordings; I understand his performances were the same way, he just didn't make mistakes.
Hamelin...as above, but his tonal pallette is more limited, his playing can tend to be stuck in the same texture or tone color throughout a piece. But his workmanship is extraordinary.
Yundi Li...he has the potential to be like the cats above, but he is very young and he needs to settle in. There are anticipated climaxes and unsteady passages in his Chopin Grand Polonaise.
Cziffra.... I hear a lot of small errors and blurry passages in many of Cziffra's recs but like Horowitz' mistakes they are largely inconsequential.
Pollini...I heard him in recital about 10 years ago, he made many mistakes, he didn't break down but they affected the flow of the music. Dreadful concert, and yes we can all be perfect in the studio.
I would also put Gould at the top of this list with Michelangeli. I agree with Mr. Ramsey (see above). In Gould's repertoire there is no way of evading mistakes.
Evidently Leopold Godowsky was hyperperfect, sadly there are no recordings. But what about.....
Josef Hofmann...at the end he was an alcoholic but his early recordings are astonishing, and before the days of the overdub; all pianists should listen to his recs, they are astonishing, and a window into another time (probably a better one, piano-wise)