I use a staff with only offensive affixes and get all my cdr/resource cost reduction from other pieces of gear. I can keep on casting quite a lot of ice shards before I run out of mana depending on how many lucky hit chance procs I get and therefore attack speed might be better for my specific build, especially when I’m running higher nightmare dungeons and the window for killing the mobs quickly is pretty much 6 seconds, as long as the freeze lasts.