So far as the comparadun/parachute/upright hackled fly thing goes, I think they all have their place and at times, each is clearly superior to the others.
But, IMO, there are common sense things that tend to help us decide when which style is best used.
For example, I believe that comparaduns are significantly superior to the other styles during the early paralep hatches. Because of the average sort of April weather and perhaps also as a characteristic of the species, paraleps tend to be less active on the water. A lot of the best paralep fishing is to fish working in off current eddies where the flies circle and they sip. In these situatuions, I've done much better with the flush profile of a comparadun than either parachutes or conventionally hackled flies.
On the other hand, it's my view that you might as well fish with a crescent wrench as a comparadun for most of the larger mayflies like March Browns, Gray Foxes and Isonychias. Also the drake. These flies tend to flop around more and, I believe, by virtue of this and their size, that a fully hackled fly is by far the most effective choice. A parachute has some utility here, but a comparadun just simply cannot do a decent job of imitating a bug of these sizes, IMO.
There are lots of other comparisons that can be made such as that comparaduns are (IMO) virtually useless in places where the wind is a significant factor and is skating the bugs around.
But by and large, I think the best choice is usually situational (wind, water type and air and water temps) with a minor, but sometimes significant role being played by characteristics of the species in question.
I don't think there is any clear better or worse among the styles...