Well.... I will take a stab at this.
Of the three you mentioned, lets start with the "Regular" rifle primer. These could be CCI 200's, Remington 91/2's etc... They are your "Standard" primer.
"Magnum" primers on the other hand were designed to be a little hotter. Some folks, and load books recommend these when using a ball type of powder. The though process behind this is that the ball powder needs a "Hotter" ignition source.
"Benchrest" or "Match" primers are normally a standard primer that has went through a lot tighter quality control.
One thing to keep in mind, all manufactures of primers are different. Loads that are safe using a Remington 91/2 may not be safe by switching to another primer. When ever making adjustments to your load and you change primer types, back off, start low and work back up.