I have both the S0 and S2, both SS. My view is that if you mainly use the native apps and don't care about GPS or the additional waterproofing, then the speed differences, at least now, are negligible. (For whatever reason, I find that the S2 is much faster with 3rd-party apps, but YMMV.) If you are in that situation, it's not rational to get the S2. I'm sticking with the S2 because I use the watch frequently, and the little things (more responsive, more water-resistant, easier to view in sunlight, GPS if/when I want to use it, etc.) over time have value, but I can see a lot of folks in the same position simply sticking with the S0 until a much better AW comes out. The S0 also is a little thinner; it's not much, but it's noticeable. Any thicker, and the S2 would be a porker. A wildcard would be changes to the OS that make the S1/S2 noticeably faster for some tasks than the S0, but that's speculation.