Me and my brother just had a Siri vs Google Now fight. We decided Siri won (much to my chagrin!).
Sending a text:
Google often didn't work, if there's multiple possible contacts you have to tap the right one, and you have to tap "send". Siri, apart from the first tap, is totally hands-free.
Literally couldn't call a contact. Asking "Call Jeff" resulted in Cool Jeff, Cola Jeff and, when Google worked it out, it again needed a tap to actually make the call. Siri worked each time and being able to say "Call my brother" is really cool.
Although we also agreed that Siri's over-humanisation got very annoying.