I think it also has to do with the type of plowing you are doing.... If you are planning on doing streets where you wouldn't have to back up as much get a manual..... If you are going to be doing parking lots and need to do alot of backing up get a auto... it would just be easier (in my opinion) to have a auto in a parking lot with a lot of backing up to do
Personally, I prefer a Stick. I do a lot of plowing on steep drives. I like the ability of controling how fast I go, without using brakes.
Now I am plowing with a Chevy 2500 - 8.1 taged to an Allison. So far, the Allison is great for driving down the road, but reverse is to slow for backing up. Still getting use to the auto for plowing, but it is still early in the season.
Considering that 98% of my work is residential, the automatic is the only way to go. Its hard enough to keep track of all the gadgets I have to use when plowing, lets see; front plow joystick, rear plow toggle switch, rear back up lights switch.