Trust me Siri is marketing gimmick. Google app voice feature is way better.
When I had my Galaxy S4 the first thing that I enabled was Google Now. After hearing all the rave reviews of it and how it was better than Siri I wanted to give it a try. I let it learn my info and habits over the course of a month. Guess what? It's not all it's cracked up to be. Yes, it is a bit faster than Siri and at times more accurate, but there were plenty of times that it was very slow and completely inaccurate when transcribing voice-to-text. And there were also a lot of things that I think it did worse than Siri did.
It's ability to predict and offer you information at the right time is good and bad. Sometimes it offered me navigation to work and helped me to avoid traffic, but it also would try to navigate me to work every time it thought I was going out. Every. Single. Time. Very annoying. Also, the card UI sucks, save for when it's displaying information at a glance. It sucks when you're trying to use it to call someone, dictate a text, etc. It was less clear than Siri's UI and it also doesn't tie into the device as much as Siri does (i.e. device settings can't be change with Google Now).
So yeah... It's not all it's cracked up to be. If you think that the voice feature in the Google Search app (which is just a watered down version of Google Now) is better than Siri, you're just being ignorant. Other than reliability, Siri is just as good, if not better than, Google Now.
EDIT: This isn't to say Siri is perfect; far from it. It just seems more refined and thought out, in my opinion.