I 'defected' to Nexus 5 after not being able to stand the slow-ass animations and other quirks of iOS 7. Stayed with that phone for 4 months and came back to the 5S... one of the main reasons?! Google Now!! let me state just two things of the 20 or so grips I had with google now...
1. Having it understand ANYTHING while driving was a colossal effort. Guaranteed to get you in a wreck. Even speaking with phone glued to my mouth.
2. Telling it to find my friend Joseph's contact would result in ALWAYS getting google.com results for Joseph <last name> and scrolling down it'd show you your phone contact! WTF is that...
3. let me throw in a third thing anyways since I'm angry again thinking about it while typing this... "OK Google"! "Set a reminder to pickup grocery when I leave here"... ...thinking thinking thinking... NOTHING.
Basically, to me google now was centered around listening to me for the sake of giving search results on google.com so it could stock me around with targeted ads later vs giving a solution to my frickin question. Asking it to set a reminder for me doesn't result in anything where google can monetize... till they find a way haha...
Siri has always been worthless (compare it to Google search via the available microphone).
It may enunciate names better, but it is so broken - unless you like hearing "Would you like me to search the Web for that" ?
Update: By the way, Siri still cannot properly understand a request to pronounce your username.