I have several of each (some AF, some MF)
Originally Posted by CanonShot
The earlier zooms were mostly MF one-touch zooms.
With MF, the one-touch is faster and "easier" to use.
With AF, there is little difference in ease/speed of use.
In the case of both, as the action 'loosens up" due to wear, particularly in the case of lenses with large, heavy, glass elements, there is a tendency for zoom creep if the lens is not level, and one needs to stop this creep by the careful application of a restraining finger (or whatever).
IF you want precise focus a two-touch is always better.
Depending on the size of your hands, size of lens and lens used; with practice one can use one part of the had for zooming (to a degree) and the other part for focusing.
With practice you will get used to going between actions without thinking.
I've found that I prefer 1-touch over 2-touch for several reasons including the wonderful DOF scale on many 1-touch zooms. That said, I also don't prefer zoom lenses.
Just personal preference, I suppose.