I found audio to be too distracting, and sort of subtracting from the more subtle intent (IMHO) of being able to feel the notification, glance at it, and return to a meeting/conversation with minimal distraction from the people I am interacting with. If my watch vibrates and I glance down, chances are they haven't seen it as me breaking my attention away from them for something that could be trivial (what? More surfing squirrel video from my wife?). If there's an alert sound that I immediately react to, people tend to notice.
I've found that I get most of my notifications. Sure, sometimes I miss one or two, but it's much better than when I just relied on my Smartphone. Setting to vibrate or silent in a meeting I would constantly miss information. In some cases, things I wished I known about a half hour sooner sat idle while I was blissfully unaware.