Didn't we already have such a poll?
I think the general result was rather clear:
The prefered switch type and position depends on 2 things:
1.) Size.
2.) Intendend use. (In other words: The type of flashlight.)
For example, you sure wouldn't want a side clicky (such as found on the C/D-sized maglights) on a single AAA-light, now wouldn't you?
Or how about a tailcap clicky on a 3-D (or bigger) sized light? No thanks, eh?
How about a twisty then? Nah? Well, except for hids maybe, since they dislike being turned on/off fast anyway.
You see where im getting at.
Besides for size, you should also think about what type of flashlight it is.
General use (in other words: 08/15 Household light) usually means side clicky.
"Tactical" use usually means tailcap clicky.
Users of Survival/Camping type lights mostly seem to prefer twistys over other switch types.
HID/Searchlight usually means it doesn't really matter, as long as the chance of accidentally turning the light on or off is extremly small, since HID's don't like being turned on and off fast.