You can't really go wrong either way. If you're going to overclock them (gigabyte's has some factory OC already), make sure you get ASUS's oc'ing tool. It works with any manufacturer. With AMD's default, you're stuck with a max core speed of 1050mhz and the 7850 can hit 1300+ with a voltage bump.
Both the windforce and the frozor have 4 eggs and some complaints. the windforce has more reviews, but newegg reviews are pretty crappy. Like I said, either card is good. Other than the DCII, those are the best stock coolers on the 7850's.
Alright im gonna go with the MSI. since both are good, and its easy to OC 7850 (so i wont be needing the factory OC).. im gonna choose the less noisy fan. Need your stamp on this people. gonna order ..