I'm willing to wager one of my spare Kirbys on your typical American carpet, that the 11 amp version of the Thunder is the best performing bagless cyclonic upright to date, and the current Rainbow is the best cleaning bagless on the market.
A properly working 11 amp Thunder filters better in the cyclones, and cleans very well. I had one outright, my bday present for my 14th bday. The only thing on that HEPA was carbon from the brushes, we only replaced it after 6 years because we felt it should be. Serial #10635 and still works.
Having used the current Rainbow, that motor is so darn powerful and coupled with the constant airflow finding a better performing bagless isn't easy.
I rank Dyson as the best in a discount store. If you go to Walmart you probably won't exceed it. Comparing it to a Fantom is irrelevant to most because you can't easily find one in great shape. Comparing it to high end vacs like Rainbow isn't fair due to cost differences.