I would bet that the weeklies have a slightly lower IV than the monthly since the crowded trade would be to buy the monthly and sell the weeklies. Much like the manner in which the call skew is flat or down attributable to the buy write crowd in a stock. Previous poster pretty much sums it up-other than the slight call flattening on the weekly (unless it is a special event like earnings week) there should be no material difference in weekly and monthly. Someonealso noted why would anyone buy weekly is they go down in value quicker-answer is gamma.