Well I'm going to go against the grain and say that I prefer Hamelin because of his unusual repertoire.
Anyways, there's no questioning Cziffra's astounding technique, but when I think "interpretive side" I don't think of Cziffra.
again, mass-debatable
hamelin allows the music to speak for itself and plays very straight
cziffra imposes his own musical temperament, ideas, colours, and rhythmic idiosyncracies, which in many pieces takes them to stratospheric levels of tension, excitement, and emotion.
for sake of comparison, compare both of their liszt 2nd polonaises...
hamelin plays it very straight, a really good standard interpretation and of course with awesome technical execution, but next to cziffra, he sounds completely uninspired, unexciting, and even boring, if you compare them back-to-back.
i think hamelin is at his best in playing music that needs a very objective approach and doesnt demand much individual input from the performer himself.