This purely an opinionated question, and fanboy's will list there company. I have to say:
DFI Lanparty UT nF4 Ultra-D
Epox 9NPA+ Ultra
Both boards are awesome OC'ers with DFI edging out since it can do memory voltages over 3.1volts which is what the Epox is limited too. Both are really really stable. But for the buck the Epox wins out of those two, you get loads of features the DFI can't offer. But on the flip side the DFI has two PCI-E x16 slots, and can be modded to SLi if you ever want to go that direction.