Both are pretty nice. Seems like Siri always pops out more visible information though which might explain the millisecond delay vs Google voice. Wasn't to pleased with Google voice when setting reminders/alarms and stopping at the menu. They need to fix that. Google voice does sound much more natural, but Siri has more natural responses.
I'll give it a tie based on the video only.
Not sure if you noticed, but Google set the reminder anyway (you can see that in the toast notification at the bottom of the screen) but offered the option to change it.
Obviously it would be better if it offered the option to change it by voice though. It could say "reminder set for 12 hours. Please say 'okay' or specify a new time." or something like that.