Just to weigh in, I've just returned my Huawei watch for an S2 classic. I haven't used Tizen, but wanted to try it out. If I like the experience, I'm going to return the S2 when the S3 comes out. I went with AW because I felt that the OK Google was just too useful to pass up on. In real life, though, I've found that I don't use voice commands very often. Honestly, when I do, it's great that it "just works," and I'll see if I get too frustrated with S Voice. But one thing that has annoyed me about android wear is the swiping-based interaction. Often when I look at my watch outside, because of the AMOLED screen, all I see is a black screen with a "T" shape of fingerprint smudges across it. Outside visibility is a limitation of these watches of course, but having to swipe all over the screen constantly has been irritating. I really like the idea of using the rotating bezel more to interact with the UI.
TL;DR: Google Now>>>>>>> S voice, but I, at least, don't actually use it enough for that to be the deciding factor.