Dyson, Hoover, central vacuum compared to my bagged cleaners
My mom once filled my Hoover T Series to the very top of the container. It had almost zero airflow at the hose. However, I have filled my Dyson to the brim before and it kept its suction. My central vacuum has a "self cleaning" filter, the kind that inverts when the machine turns on and drops down when it turns off. It looses suction power somewhat quickly compared to cyclonic vacuums, especially after dry cleaning the carpet.
On the other hand, my Oreck never seems to lose cleaning power (it doesn't have a hose, of course, so I can't really tell if it loses suction) and my Eureka Surface Max canister vacuum only loses suction when the dirt covers the hole of the bag (it does, of course, lose some suction before that but the majority of the suction is lost when the bag is full).
I recently decided that I prefer bagged vacuums, with the exception of my central vacuum and my Dyson. My central vacuum only has to be emptied occasionally, and it keeps most of its suction for a while. My Dyson doesn't loose suction until the dirt starts covering the shroud.