SeboFan is correct!
Top Selling and Top performing are 2 different things.
Top Selling right now is most likely based on the following:
1) Price-- the economy is awful
2) What's on sale-- The primary reason why Kenmore has been mentioned by Consumer Reports as being the most popularly selling canisters, is that nearly every Sunday and many times on Thursdays, for the past 25+ years, there is a picture of at least 1 Kenmore canister on sale in a Sears circular. Even when Hoover and Eureka canisters were sold in department stores, the appearance of them in a competitors circular was quite infrequent.
3) Many consumers shop at Wal-Mart
4) Bagless- people think that seeing the dirt in the cup and having to empty it each time means its cleaning better than bagged. They don't realize how much smaller the dirt cups are the lack of ability of a bagless vacuum to compact the dirt in as would be in a bagged upright. For pet owners, bagless is quite a benefit, because pet hair fills bags quickly. But for deep cleaning of deep down dirt and dust bagged works out better for capturing the dust and not clogging a filter.
There are some Hoovers and Eurekas on the market that do advertise on the box that they outclean a Dyson. This is usually mentioned along with a percentage of by how much more and is supposed to be backed by facts of ASTM Testing. ASTM is an independent testing agency based on various tests by different methods, each with a different test number, example F2609. This testing is creditable with controlled variables unlike those of Consumer Reports whose test methods may change yearly and use substances like Talcum powder which clogs filter pores quickly immediately draining power. However at the same time all vacuum models are different. A Hoover Decade 800 cleans different than a Hoover Elite which cleans different than a Windtunnel T, which cleans different than an Anniversary Windtunnel canister, etc. The same is for Dysons and any other brand. I have had great results with many models of a brand while receiving unimpressive with other brands. Suction, Airflow, Agitation, Edge Cleaning, location of and size of suction duct in agitator cavity, softness of bristles, arrangement, and length of bristle extending below base plate are all factors involved in cleaning ability. Some models perform better on commercial indoor/outdoor carpet, others perform better on plush, others perform better on loose weave.
A perfect vacuum of all surfaces and a real evaluation of a vacuum for ones environment requires a trip to your local vacuum store where with expert advice and experimenting with various machines one can look at design differences and decide what will perform best and makes sense for the surfaces, layout of owners property and usability for that owner.