The 8K7A has an onboard POST reader, which costs about $30 as a PCI card, and has 6 PCI slots. It includes a rear bracket to take advantage of the extra USB ports, too. Downsides: 2-phase power supply (but it's heatsinked, so high-end T-birds still run), it supplies too much voltage to the CPU (I get 1.81v where I should have 1.75v), and it doesn't have AGP voltage control (although it's documented to have it). CPU's tend to run hotter in 8K7A's than any other SocketA boards. The 8K7A+ board has a (crappy) HPT-370 RAID controller. The non-RAID version is a great value at $130.
The 7DXR has 3 DDR DIMM slots, AGP Pro, a better-colored PCB, and better documentation. It may/may not be more stable. It is documented to be Palomino-compatible. The RAID controller is the marginally better Promise unit. It also has better CPU temperature monitoring (better thermistor that makes contact with the downside of the CPU). Downsides: $60-$70 more expensive, 5 PCI slots, no POST reader (more useful, IMHO, than IDE RAID), short supply.
Am I happy with my 8K7A? Since I was able to easily buy it, it was inexpensive, and my system hasn't had an unexplained bluescreen in the past two weeks I've been using it (Disclaimer: ECC memory and Windows 2000), I'm very happy with it.