S6 has a new sensor and way better accuracy. It looks different and has a new design. In sports world at least, this is considered as a new sensor, but Apple is not that into sports hahaaa. Also take a look at DesFit's video of the S6. He does a lot of mountain biking. A very hard sport for OHR to be accurate because of vibrations etc. It was close to the new Garmin HRM Pro chest strap which says everything. Very, very impressive. If money is not THAT big of a deal, GO WITH THE S6.