What determines which system you use?

Pie Man really started this line in the
 "I didn't know anyone still did shorthand." thread, by saying:
"I wish I knew Gregg AND Pitman. Hell, I wish I knew Gregg enough to take notes with it. What determines which system you use?
I was looking at various shorthand systems today (with vastly newly opened eyes, let me tell you) and laughed out loud in the library at the preface of one book, two paragraphs in length. It was written by an earl who was a Pitman writer. I think he used words like "light-line abominations" "beauty of geometric styles" and "ugly single slant styles".
Another author talked about how he had recommended a light-line cursive single slant version and then got complaints about writers' cramp from the students and teachers at the school to which he had recommended it. He said Pitman writers never get writer's cramp because they move the hand up and down in relation to the line, and change the pressure of the pen when writing shaded characters. (This conclusion based on an unspecified number of complaints, and five students who came to him begging to learn Pitman, because they got writer's cramp from the light-line method.)
All this to say that in the absence of actual scientific study -- which I do not think anyone has yet done -- determining which system (or subsystem) you prefer is entirely in your own hands.
I'm fairly sure that my statement that I do not think anyone has done any actual scientific study will be disputed.
Where is Psetus when we need him?

(by sidhetaba for everyone)