i have a windows phone but have used the three major os's recently, and while google now is the most helpful, cortana is the most like a real person, and siri comes last for being an all rounder, that isn't that great.
PS ShadowLea, i love the windows phone ui, even if the rest of the phone is still playing catch-up
Wife just got an iphone 6. Siri is trash. Google Now actually understands what you need to ask and can "translate" your phonetic and contextual mistakes and work through them. Siri just sits there with her finger up her nose. Siri was and remains a novelty.
I've tried both and, I like how you can actually speak to Siri like to a real person, you know you can say hello, goodbye etc. etc. And in Google Now such things are lacking. On the other hand I prefer Google Now.