If you only rock it "one way" I agree, but that that aint nescessarily so if you need to rock "both ways" (shift between forward and reverse gear as you rock). Auto or manual, which one is easiest would depend on how smooth the gear shift lever is and how complicated that movement is. All other things being equal, the clutch in - change into reverse - clutch out procedure is more complicated than just push the auto from "D" to "R".

The by far easiest car I've ever rocked this way was a Dodge minivan (grand caravan) with gear level on the steering wheel column. If you pull the gear level towards you, the locking disengages and it is the simplest "two-bumps" movement. One hand on the gear level, one hand steering and no foot movement to syncronize except the tiniest up-and-down motion of the accelerator. Sweet as a breeze... Autos with the level between the seats are usually more complicated, you have to move in a zig-zag pattern to go from "D" to "R".

Althoug I love stick shifts, most autos are very good at providing the softest, slowest possible start with no wheel spinning at slippery roads. Just pretend you've got a rotten grape between your foot and the accelerator, anything but the softest push will crush that grape...

Once, I failed miserably to rock out a manual transmission car because the oil in the gear box was rather stiff at -20 celsius (-4F). Having started the car just one minute ago I was turning into the driveway to pick up someone. As I stopped I felt the front wheel were digging into the snow. If I had slammed immediately into reverse I would have rocked out of there before the wheels had time to crush themself deeper into the snow, no problem at all. Because of the sluggish gearbox oil changing gears took about 5 seconds... bummer! Stuck!