Like some here, i too went from S4 to X10i to S4 II. For me, i never found a good fit for the X10i and the sound was good, but that was about it. The S4 may lack some delicate detail, but it is more exciting to listen to (esp. when i use it for commute). Strangely, the S4 fit my ears better and provide a consistent seal vs. the X10i. In addition, there is more wire noise with the X10i when i use it to exercise.