The original question...
About efficiency in cyclonic filtration...Yes, Dyson does have the best system right now because he's had longer to work with it than any other manufacturer. Like Air-Way and the disposable bag, Air-Way had it perfected before anyone else could even attempt it.
Electrolux/Eureka currently sell a multi-cyclonic upright and a multi-cyclonic straight suction canister. Apart from those two, Eureka also makes several dual cyclonic machines as well as single cyclone models. One problem is that Eureka is advertising machine as "multi-cyclonic" when in fact they are simply dual cyclonic. True multi-cyclonic models have more than one high efficiency cyclone.
Hoover makes dual cyclonic as well as multi-cyclonic models. The WindtunnelMAX is an example of a great multi-cyclonic. Most of Hoover's machines are simple dual cyclonic uprights - with a poorly designed shroud that allows quantities of lint to pass through and ultimately clog the pre-motor filter. Hoover's best multi-cyclonic upright (and canister) models still pass a large amount of fine dust onto the pre-motor filter.
Shark makes single cyclonic models, and loads their filters with dirt.
Panasonic makes several very nice multi-cyclonic models - but the high efficiency cyclones are not designed correctly, and pass a fairly large quantity of fine dust onto the pre-motor filter. Panasonic's cyclones are very easy to take apart for a good washing. Our Kenmore models are made by Panasonic, and use the same cyclone systems.
Bissell's Healthy Home and Heavy Duty models are true multi-cyclonic models and filter quite well. Bissell seems to be dividing their line up between fairly good multi-cyclonic uprights and terrible single cyclonic uprights (in their low priced line). They also make several dual cyclonic models, but these have a small high efficiency cyclone and don't work as well as a DC01 at filtering fine dust.
Dirt Devil, Hoover, and Eureka all offer a canister, multi-cyclonic, that appears to be made by the same company in China (King Clean). The parts are interchangeable. The cords are too short, and many have motor problems right away.
So, to answer the question, Dyson still has the best separation system in true multi-cyclonic vacuums today. That will all change here in a few months when Tacony launches their new Fuller Brush Multi-Cyclonic upright. Anyone attending the Vacuum Collector's Convention at the Vacuum Museum in June, will get a chance to see and use the new Multi-Cyclonic upright prototype. The engineering department has really been working hard to make the best cleaning and best filtering multi-cyclonic available.