Cortana vs Google Now

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 Now
From knowing the weather before you start your day, to planning the best route to avoid traffic, or even checking your favorite team’s score while they’re playing, get the information you want, when you need it.
Face to face in the news:

2015 - Microsoft will bring Cortana to Android and iOS. Google Now keeps calm

Microsoft announced that both Android and iOS devices will be getting access to a companion app that gives them access to content from their Windows 10 PC from whatever device they choose – and Cortana is coming along for the ride, too. Cortana is also included in Windows 10 on the desktop and you’ll be able to set it up to work with both Android and iOS devices when the companion goes live, too. On Android, it’ll exist as a separate dedicated app (iOS support was only shown as ‘coming soon,’ but it may live inside the Windows 10 companion app instead of as a separate destination). On Android, Microsoft showed it providing weather forecast information, and setting a reminder, plus providing a follow-up alert for said reminder later on.