IMHO it sanctuary the same really. But asus definitely is better because it's quieter and more stable but still I would go for the cheaper one and I recommend getting the top version of asus as its better. If you can take a look at the EVGA GTX 670 FTW versions they are pretty good as well with their excellent customer service and RMA.
the asus runs a bit quieter but then the power edition will overclock further due to some binning. if we were talking about the discontinued TOP edition and a locked power edition, the TOP edition will overclock further
id get the msi as of now though. its a fair bit cheaper for about the same thing. also, the evga ftw is out of the question with its much cheaper 680 reference cooler and pcb.