I can say for sure that pretty much no one has surpassed the greats of the 20th century in terms of technique. Cziffra's Grand Galop Chromatique comes to mind -- no one I've seen today can do what he did with the piece.
That said, I prefer the older pianists in general for a few reasons. There wasn't as much emphasis on note-perfect accuracy, and there was more scope for genuinely interesting interpretations imo. On a scale from 1-10, I'd rate Horowitz a genuine 10, one of the greats of the last century.