I went through the exact same thing. It was one of the hardest decisions in my life.
In the end I decided to go with Gigabyte z77x-d3h because it has "all Digital Voltage, Frequency and Phase Control".
Asrock z77 extreme4 also claims to have digital voltage control but I read many forum posts saying that it's not really digital. Google it. You will find the posts.
Also, I trust Gigabyte board's durability more. My other gigabyte board is still working fine after enduring 4 years in a really hot and dusty environment.
But this is really a biased opinion, as I have no experience with Asrock boards.
My 3570k is currently overclocked to 4.4. It's stable, passed all torture tests without errors, and the temperature doesn't go over 65c during gaming, using Hyper 212 EVO(single fan).
All I did was change the multiplier to 44 in BIOS. Voltage and all that other stuff are auto adjusted by the mobo since I am a complete noob when it comes to OCing. From what I can tell, the mobo isn't overcompensating on the voltage, which some motherboards do when they are set to auto.
Boot time is incredibly fast too.
I don't regret my decision one bit.
Oh almost forgot, I actually had a problem trying to get my Crucial 8GB 1600mhz ram to actually run at 1600mhz. The motherboard kept setting it to 1333mhz no matter what I tried. I had to update the BIOS to the latest version, F9, to get it to work at 1600mhz.