Would you rather have a band play old material that you can sing along with or new material you've never heard at a concert?

I saw a show the other night, and John Darnielle, lead singer of the Mountain Goats, asked the audience if they would rather hear old material or newer (or more obscure material). I like singing along, but it can be valuable to hear things that you can’t listen to on your iPod as well. What would you rather hear? All of one, or a good balance of both? Is it bad for artists to be promoting their new music without acknowledging the old stuff that brought the people there to hear them?

Sorry if this has been asked before; I did a few searches and didn’t find it…