I think some of the reasons that Google Now is good vs Siri is because it actively "guesses" what you need, while Siri is something you need to constantly ask things of. Google Now alerts you with things before you even think of asking them.
However, one of the big hurdle Siri faces is its reliance on always-on connectivity. Without a data connection, Siri can't even perform offline functions on your phone (like setting reminders, opening apps, playing music that's stored in your library) which also hurts perception of its use when you're limited for connectivity (low signal areas or plain not having data because being abroad). I don't know how Google Now fares in this capacity, not having really used it.
Anyway, I've disabled Siri, much less time consuming to just touch my way to things than ask it, wait for it to analyse what I want, ask for a confirmation, wait for it to analyse my confirmation.