I've had four of these 990FX boards and am currently with the CHV-F.
The Gigabyte UD3 is a cheap board masquerading as a mid-high overclocker's board. Yes it has a very good layout and yes it has a nice colour-scheme and yes Gigabyte are very good with their bios updates......all the reasons why i bought one.
Unfortunately when you hold one in your hands it instantly becomes obvious that they've cheaped out on the component spec. The voltage are all over the place and they are one of the least consistent set of boards (including UD5 and UD7) i've ever seen.
It really is not designed to handle the power of the FX line of CPU. This is why they blow up as often as they do and Gigabyte have seen fit to add all sorts of fancy throttling to the bios over and above the scramble to tack on LLC as a revision to their early boards. This was such a frustrating time as the board took SO much fiddling with just to be consistent. Lets not talk about the fact that you could fry an egg on the NB heatsink and the software voltages were just not as Gigabyte would have us believe. I think that what they are telling us is the NB temperature is the VRM temperature and they were trying to hide the fact that the VRM heatsink is inadequate. KK will be along in a bit to put you straight with 'facts' though.
UD5. I have one of these in a second machine and while it's got better heatsinks than the UD3 it's just worse (so much worse) with it's voltages. This one has a mild OC so the nutty voltages don't matter so much but if it was in my main machine it'd be sold already.
UD7. Was completely put of this by how poor the UD5 and UD3 were and when i saw one physically i could tell it wasn't a leap above it's siblings so likely to be just as underwhelming.
Sabertooth. I got this one after the UD3 blew up it's VRM and took out my FX with it. Immediately i could see it was built a million times better than the UD3 and UD5. It overclocked brilliantly too and more importantly was stable at high OC. The only real gripe i had with it was that the slot layout was a bit mental and eventually did not fit my needs with CFX, audio and additional LAN cards. I was always a bit disappointed that the fan headers only worked with PWM fans too if you wanted to control using the bios.
CHV-F. Using this now. Except for little things like bios control of 3 and 4 pin fans there is not much difference in the real world to the Sabertooth except for more flexible slot layout. I can tell it's built a bit more 'beefy' than the Sabertooth but i don't think those who OC on air will see the difference or the benefit. Comes down to price, slot layout and colour basically. It does have fancy audio and an intel NIC but people with the funds to pay for this board are just as likely to have dedicated audio and LAN cards anyway. If you don't have these cards but want a bit better performance from these things then it might be worth it.
With both the Sabertooth and the CHV-F, Asus have brought out new boards and it disappoints me that they have basically stopped bios updates for the old models which i see is trying to force existing owners onto the new ones. They took a while to update the bios for the new revision of FX and there was talk that Asus tried not to update the old boards for latest FX...whether that's true or not who knows but they did take a while to update compared to other manufacturers. The simply have not updated the RAM compatibility lists despite the improvement in speeds and capacity we've seen over the last 18 months. the cynic in me says this is to do with the new boards making a big deal about their ability to run fast RAM......
IMHO, the hardware of the Asus boards are much better than the Gigabyte but the bios support of the Gigabyte is better than the Asus. I think that the hardware of the Gigabyte is so bad no amount of bios support is going to make up for it. I've had Gigabyte for years, multiple different models and i have preferred them up to now. For me, they dropped the ball this round.
I'm not trying to tell you which one to go for but simply inform of my experiences and observations of ownership of the three. Good luck with your choice.