Ed Martin wins in a close one. I haven't seen any polling, so this is little more than betting on your favorite team to win.
For the past decade or three, only 1 in 10 blacks have voted Republican. I think that will change Tuesday. My conservative estimate (based on a PJTV poll) is 1 in 4 blacks will vote Republican. This will be the news story Tuesday evening and will cause significant problems for the Democrats over the next two years. Depending on where that 25% is distributed—it wont be evenly distributed and I think there will be areas of Georgia where Republicans get 33% or more of the black vote—depending on the distribution, Republicans may pick up some seats in close districts. Missouri's Third Congressional District (Ed Martin vs Russ Carnahan) might be one of them. About 9% of MO-3's population is black.
As I've said before, I don't think the GOP has done a very good job courting the African American vote. The establishment changes slowly, but if Republicans net 25%+ of the black vote on Tuesday, the Republican Party will notice and, hopefully, change faster.
Here are a couple of videos I've put together for fellow conservatives who happen to be black. The simple message is: "We want your vote. Vote Republican."