The Samsung Galaxy S3 is the much better phone. Much smoother, no bugs and no bloatware. The SGS3 also has more RAM.
If the HTC One X is anything to go by then the One X+ will most likely have buggy software and occasional but annoying lag. Some versions of the HTC One X can't record videos at 19 FPS because of poor camera build quality. The most commendable thing about the HTC One X is the screen.
However I think the advantages of the SGS3 outweigh those of the HTC One X.