Probs the next Nexus or some HTC at the end of 2013. Never had a single problem with One X.
I've been playing with numerous other devices at work and they never quite get there where Sense 4+ and HTC is now. At least Samsung feels so much plastc. Actually broke one SGS3 preview sample by trying to bend it and compare the quality with One X+, lol. Sonys phones are quite good, yeah, but I'm not a fond of their looks. And uncreatively they all look alike. Can't tell Xperia S, T, V, etc. apart form a distance.
HTC making next Nexus would be more than perfect, but unlikely..
Phone: Nexus 5 - 32Gb - Purity
Tablet: Nexus 7 (2013) - 32Gb - Purity
Past: HTC Incredible S, HTC One X, ASUS Transformer TF700