Cortana vs Google Assistant

Cortana is your personal assistant on your Windows Phone. She's there to help make things easier for you and keep you up to date on the things that matter to you. Whether it’s to keep you looped in with your world or help you manage your everyday life, Cortana is there for you.
Google Assistant
Virtual assistant integrated in conversational user interface products: Google Allo and Google Home. You can ask a question for an answer, and follow up with multiple questions, with Google picking the conversation out and returning the right answer.
Face to face in the news:

2017 - Cortana arrived in Skype to keep up with Google Assistant

Microsoft’s virtual assistant Cortana has finally arrived in Skype, offering users in-context assistance during their chats, as well as the option to message Cortana directly to ask questions or get help with a number of other tasks. The idea to bring an A.I.-like helper to mobile messaging isn’t unique to Microsoft. Google’s Allo app is aided by Google Assistant, while Facebook Messenger has its own assistant, “M,” for example. Cortana can offer other input, like restaurant options, movie reviews, a good place to meet, a fact it knows the answer to, and more. Plus, the assistant can help with scheduling events and setting up reminders, which are then synced to your other devices where Cortana is enabled, like your Windows 10 PC.

2016 - Microsoft redesigned Cortana for iPhone and Android to catch up with Google Assistant

Virtual assistant Cortana is still not very popular on iOS and Android. So Microsoft decided to redesign it. With Cortana’s makeover, the more popular “quick actions,” as they’re called, have been given a more prominent position. While you still access them with a tap from the main screen, those things you do the most — like viewing your day, viewing or setting reminders, checking meetings and reading the news — have moved to the front of the experience. The black-and-white theme is gone in favor of a very purple one. And, under the hood, Microsoft has made speed improvements so the app feels faster than before.

2016 - Google Assistant arrives in new messenger Allo to challenge Cortana

Google is launching Allo, its AI-centric messaging app for iOS and Android that contains Google Assistant, the new conversational assistant. Google Assistant is much more than a simple messaging bot, which tend to have a fairly limited set of capabilities. There are two ways to interact with Google Assistant. You can chat with it directly — Assistant appears alongside your other conversations in the app — or you can call it up while you're chatting with friends by starting a message with @Google. In both cases, it can help with many things that you would use a quick Google search for (think translations, conversions, directions, flight statuses etc.) and even has a few extra tricks, like (again) photo recognition. It's still in a "preview" stage, according to Google, who plans to bring the feature to many more products in the future.

2015 - Microsoft announced voice-enabled Big Data platform Cortana Analytics Suite to compete with Google Assistant

Microsoft announced Cortana Analytics Suite that includes Azure ML, the company’s cloud machine learning product, PowerBI, its data visualization tool and Azure Data Catalog, a service designed for sharing and surfacing data stores inside a company. It’s a service that associates data from multiple sources on-demand, using some of the analytics technology it had developed for Power BI to make everyday data queriable by voice and accessible through touch. As for Cortana, which is the Microsoft voice-driven personal assistant tool in Windows 10, it’s a small part of the solution, but Sirosh says Microsoft named the suite after it because it symbolizes the contextualized intelligence that the company hopes to deliver across the entire suite.