There are some differences but I think they surround the use or lack there of a Samsung phone. So it's more about apps and features associated with apps that Samsung has built into TW. I'll give you an example and why I chose the S2 vs AW. In TW there is the ability to snooze calendar notifications via a swipe input. It's called scheduler. That's important to me. That doesn't exist in AOSP. Also while another poster did mention installing AW allows for reply to texts via Hangouts, I've seen other threads that indicate its not without issue. If you are using a Galaxy phone get the S2 . if you are using another phone buy the S2 and give it a try. But I suspect you'll head back to AW. I use Ant+ so I'll be on the Galaxy line until its no longer supported.
Won't go to AW until they make the navigation more like this one. I'd just have no watch than AW. I'm all about making do though so could be fine but things like not being able to read a full text on the watch would be a bummer. And I read a few ppl say that was the case. : |. That could be a deal-killer. Also heard can only reject calls but can't accept. That I could live with.