Believe it or not, a slower-moving hurricane is more dangerous. It lingers over an area longer, causing more wind damage. And it can dump more rainwater on an area as well, which leads to more flooding.
Flooding can sometimes cause even more destruction than powerful wind gusts. Many of the casualties from large destructive hurricanes are the result of rising floodwaters and storm surge which can isolate people in areas where they can no longer find dry ground to seek shelter.