This is a great topic!
The answer depends very much on the species, it's mood at a particular time, the line, the fly, the conditions, etc. There is no easy answer to this seemingly simple question. "Act on gut feel and iterate to success" would be my motto.
For instance in salmon/steelhead fishing the presentation is primarily in the swing, not in the strip. It's not about stripping the fly here at all, it's more about understanding the flow and the way the line and fly interact with it.
For dries in a stream, it's mostly about drifting.
Streamers in a pond - stripping and twitching.
Stripers... perhaps the most strip-conscious fishery out there. There are as many retrieves are there are situations, and I mix it up the whole time while fishing a single spot. My least used retrieve is the double handed strip. I have a bunch of variants of the single handed strip and use pet names for them, like the dog lick or the old man or the shock and stop. I use these metaphors when communicating the strip technique to others. One things for sure - the strip does make a big difference in striper fishing.