Hi newcomer and welcome to the Tom's hardware forum.
1- ASUS is the best option, very good quality, reliability and performance.
2- The UD7 is more expensive that the ASUS, so, why spend $349.99 in a Gigabyte mobo, if with the ASUS P6X58D Premium U can get the same performance?
3- The UD5 is a very good option, more cheap that the ASUS. BUT as the UD3R don't support USB 3.0 when U use Crossfire, so, Are U planing use Crossfire with only two GPUs?
4- The UD3R is a very good option price/performance, but with the same problem that his big sister the UD7.
If you want a very good mobo for your rirg, the ASUS P6X58D Premium is the best option for U (IMO), because the UD7 is more expensive and like I say up, U can get the same performance with the ASUS.
The motherboards you have picked are all of good/excellent quality, and will perform well.
I have used Gigabyte in the past with good results, but I don't like the 'Plus' and 'Minus' setup their Bios' (used to?) have. The way this works(ed?) is that for many parameters - like voltages - the standard/default values are considered to be 'Zero', and you have to make adjustments in terms of adding or subtracting from the default. So, if the default voltage for the processor is 1.2v, you don't see that in the Bios but rather it's on you to know that without being told. So as you're working, if you have a need to increase the voltage then you don't just dial in 1.25 for the CPU. The setting you have to use is +0.05.
Many people don't have a problem with this, and to be clear it's simply a different way of going about the same task. But in my little mind, I want to know where I am rather than how far I moved from some number which I may or may not remember. So I prefer Bios' to work like the ASUS's and DFI's, where if you want 1.25v, then you set 1.25v.