I like Siri, but Google Search (free) is definitely an alternative worth considering. Last week Google released version 4.0 which now lets you have a "smarter conversation with Google." For example, you can ask, "What's the weather like?" and Google will return information about the current weather. But then you can ask a follow-up question that depends on the earlier question for context. You can say, "How about this weekend?" and the app will understand that you're asking what the weather will be like this weekend. The ability of Google Search to use previous questions as context for understanding is an impressive step in adding intelligence to these handy voice-controlled assistants. A review on ZDNet says that the capabilities of Google Search "embarrass Siri," which the reviewer now finds to be "woefully inadequate."
The new version of Google Search also adds the predictive features of Google Now. Cards appear at the bottom of the screen related to previous searches and to other context, such as using GPS to figure out you're in your car and may need an alert to traffic congestion ahead. Interestingly, Apple has brought predictive intelligence to CarPlay but not yet to Siri on iOS. Based on your previous queries, the Google Now feature of Google Search learns your favorite topics, your upcoming trips, and your favorite authors and blogs, and offers up articles and information related to them.
While Google Search might compare favorably to Siri, it certainly is a convenience to simply be able to hold the Home button to call Siri to action. With Google Search, the app needs to be open. You can either tap the microphone or simply say, "Okay, Google."
With the arrival of iOS 7, the default search engine for Siri became Microsoft's Bing. But more and more, Apple is trying to give Siri the intelligence to answer your questions without falling back on a simple web search. However, if you prefer searching Google rather than Bing, Google Search may be a good choice.
And here's a tip: Even though the default search for Siri is Bing, you can still use Siri to access Google's search by simply saying, "Google" or "Search Google" when you begin your query.
In any case, it's probably worth your while to play a bit with Google Search to get a sense for how smart these voice assistants are becoming.