How about this: roll a six-sided die. 1 or 2, get the Sapphire. 3 or 4, get the XFX. 5 or 6, get the Gigabyte.
The Gigabyte overclocks excellently, but I've heard that it is known to have coil whine problems.
Exclude the MSI, any reason why?? Also, I personally do not want to go with sapphire due to what i hear about their service. If i received a bad card from them i dont want to wait months for a RMA (heard of people waiting 6 months!!