As an Android user, I've found that Siri tends to be generally better than Google Now. I don't usually ask my phone for trivia, but rather to do something. Most of the time I'll get routed to a search query when I'm looking to command the phone instead.

This is somewhat frustrating if you don't know the magic incantation to make Google Now do what you are asking it to do. Siri's engineers have done a better job anticipating the various forms of the commands and handling nearly all of them.