I am not sure.
I only play with 2 rule sets at the moment.
Both as PDF’s in their original format but also both printed for ease.
I think that I prefer the printed form.
Maybe this is because they are thin books so there is no need to use some of the features that PDFs offer such as being able to search an entire book for certain keywords?
Maybe I prefer them as they are always on, and if I suddenly have the need to know something I swivel my chair and pick up the book, this is quicker than firing up my notepad and then opening the PDF.
Having said that, I do like the security of a PDF copy backed up onto a number of drives.
That said, the rules I use are simple enough that after a few games I need not refer to them except for the odd glance to a QRS.