The Asus DCUII but it's a three card slot. The Gigabyte Windforce is a two slot card.
If your planning on going with SLI down the road and you don't have six slots to burn for two cards then you'll want to go with the Gigabyte.
However if your have the space and aren't going to using any of the other PCI slots for audio cards etc OR are not going to go with an SLI system, then the ASUS DCUII would be my choice.
You didn't list your specs so I'm not even sure if you have an 850 Watt PSU or not anyway to SLI in the first place or even if your mother board can handle SLI or not.
Between ASUS and Gigabyte, I'vepreferredreffered ASUS. Between these two they quietest among amongst all the types. Hard to say since I've not owned either. I have however read many ASUS users saying how quite they are.
Find the ASUS DCUII Club
thread on OCN, I'm sure it will be biased to some degree but they can assure you of noise level. They are very enthusiastic about their cards for both Nvidia and AMD.