The only comparison to Horowitz could be some pianist never recorded, like liszt or Anton Rubinstein. Most people actually don't realise how good horowitz was. As an arranger, he was top notch. He could do anything at all, especially in his younger years at the piano, and improvised like a mad man apparently. Another thing most people don't realize is that though he only played only a limited rep publicly, and recorded the same, he could actually play all the standard repertoire from memory if pressed (except for Bach). The difference between horowitz and the other two is that he could play a piece at a much slower tempo, and blow the whole world of music away technically and otherwise.
I won't speak of Hamelin because he is still alive and active and a respectable pianist who has accomplished more in his life than almost anyone on earth. I hope to meet him one da!
Cziffra was mechanically great, but also a bad musician. Who would ever want to hear him play Mozart? His ease at the keyboard for running up and down relentlessly is impressive, but there are many, many pianists who can do that, even today. Horowitz certainly could! But if you listen to Cziffra improvizing, it is really a bunch of noisy, impressive garbage that gives no impression of deep musical understanding. I mean, he played jazz but couldn't swing! Have you seen his etudes? Yes they are difficult, but all flash and no reason, he didn't understand the concept of a musical 'effect'.