I would recommend you go for the long dust cover, for no other reason than you can always evolve backwards to a short dust cover, but a short dust cover will not grow into a long dust cover.
It kind of sounds like you are going to purchase someone elses project, there may be nothing wrong with it, but it does not hold the characteristics that you will eventually define by your shooting style as it evolves, or the firearm accutrements that favor the style you develop.
An Edge would be a great standard to start with....
Prices between long and short are similar.
