Dyson
For me is like any other bagless machine, you are not saving anything if you have allergies. As described above, no matter how careful you are at emptying the machine, you still have a cloud of dust in the air.
Consumer Reports rates the Oreck XL 21, the most expensive Oreck to clean as well as the Dyson with fewer repairs. I don't always think Consumer Reports has the best ratings out there, but they still did not think it was an overly great deep cleaner and failed miserably at pet hair removal.
I wonder what the new Bissel Healthy Home vacuum is like, again bagless, so I want no part of that, but it does seem to be well built. Not unlike the Dyson, the onboard tools are useless...nothing like a good old Kirby, Eureka, Electrolux, GE, Sunbeam, Air-Way, Filter Queen, Royal, or Rainbow if you want good tools. Bagged verses bagless, will always win for me.
Morgan