Re: roller plotter or parallel rulers?
I also think you need both rolling and parallel for different occasions - course planning and actual plotting. When you are plotting, keep in mind that you are not using a large stationary desk, you may be trying to hang-on as the boat is rolling and you are trying to plot a course with one and a half hands.
Its a personal preference, but for plotting I find the rolling ones more convenient (one hand). For planning either a protractor, a parallel or a combination would do. Get familiar with all of them and you will eventually settle on a preferred one.