Of the choices, yes definitely Davis.
But if we canot kill off Sherman, just because it would be too obvious (agreeing with dante), could we do the next best thing and kill off Thomas?
In the campaign proper, Thomas prevented Sherman from making at least 2 horrible frontal assaults. In TTL, Sherman will still reach Atlanta, but perhaps a week later and with easily 10,000 fewer men. This is assuming that any of the vastly lesser commanders of the AotC does not make any stupid blunders that stop the campaign before then.
If the campaign lasts all the way up to Peachtree Creek, then with no Thomas, the AotC is caught napping, and even Hood can implement Johnston's plan. It almost worked in OTL, and failed because Thomas had enough presence of mind to ready the artillery, and exerted great personal force on his men. With neither of these, the flank falls apart and Sherman has to postpone his railroad-destroying trip to keep the armies intact.
At the very least, all of this will buy Johnston/Hood enough time for Forrest to come east and start making real raids against Sherman's RR. With some better luck.....well, in OTL by the time the armies reached Atlanta, Sherman only had 100,000 men versus Johnston's 70,000. With no strong Army commander, the Union forces could be crushed in detai.