The consensus is.... the holl-ee ball is the winner!
Thanks to this thread, I got a hol-ee roller and filled it with a plastic cat toy. And Buffy does LOVE it. But somehow she has managed to chew off some of the little plastic pieces of the cat toy, so I'm not sure about that toy. Maybe we need to find a new thingy to put inside.
. Off to Petsmart today...