ATI Radeon HD 7970 ASUS , Sapphire or XFX

Hi guys, a few day ago I was trying to buy me a card AMD 7970 but the seller said me what kind of 7970 I want and said that are ASUS, sapphire and XFX, he said that is the same AMD 7970 but was ensambled by differents companies, then I want to ask you.

Which is better? and also what kind of motherboard will be better If want to use 2 X 7970.

this were my options

ASUS HD 7970 DirectCU II TOP 3GB GDDR5 (HD7970-DC2T-3GD5)
PCI Express x16 3.0, ATI Radeon HD 7970 3072 Мб


Sapphire HD 7970 OC 3GB GDDR5 (11197-03)
PCI Express x16 3.0, ATI Radeon HD 7970 3072 Мб

XFX HD 7970 Black Edition 3GB GDDR5 (FX-797A-TDBC)
PCI Express x16 3.0, ATI Radeon HD 7970 3072 Мб

thnx