Rumor is the 6S is already waterproof...Apple just won't officially confirm it. I had the 6+, the previous generation to the S and I can confirm it's not
After spending a few days tweaking the S4, adding apps, etc I can't say that I'm not that much of a fan. There are some things that are nice like widgets on the home screen(s) and the SD slot really is awesome. Other than that, I feel like the interface is not as intuitive as iOS and there are way too many configuration options for the average user...not only that but they aren't centralized. Some are in the app, some are in system settings in various spots, and some you just have to know to engage the contextual menu. I keep getting nags in the store about installing virus protection too
Navigation is also inconsistent. Sometimes you hit the arrow back on the screen, sometimes the dedicated back button. If you hit the latter when you should've hit the other, you end up totally out of the app or set of screens you were on.
I'm sure part of it is just getting used to the UI since I've been using iOS for so long but I use a lot of gadget and UI's and done my fair share of evaluating them and/or testing them so I would say that I have a pretty good handle on UI's in general. I can say with certainty that the apps for iOS are much more polished than their Android counterparts. Facebook, messaging, myFitnessPal, etc are all more clunky.
All that said, would I move to Android? The short answer is no simply because I'm heavily invested in the Apple ecosystem with the watch, iPad, Mac and my wife has an iPhone so we can connect on various apps and stay in sync. The worst thing about not having the iPhone is the watch becomes really nothing more that a digital watch. I guess I can break out some of the nice watches I have sitting around, collecting dust.
If I wasn't in bed with Apple already, I definitely would consider an Android phone. Most of the apps I use pretty regularly are available on Android except for a few. I use an app called mSecure to keep track of all passwords, financial account #'s, etc and it's not available on Android which is bummer because I rely on that all the time to look up passwords and stuff. At least it's on my iPad.