Google Home. Like the idea of being able to control Google Cast, looks like it will help the audiocast vision presented last year. I also like the physical design. However, I am not sure I like the idea of having to say "Ok Google" or "Hey Google" as the trigger as opposed to saying "Alexa." 

Given Amazon's lead, I think it is going to come down to price and the amount of integration with IoT devices. 

IoT is key because without it, for many people a room-based voice assistance doesn't have a use case that is compelling for many people. 

P.S. I wonder if the reason why the I/O event is on Google's campus has something to do with Google Home?