Wow, a lot of passion on both sides!
It's no different in anything else. Cars, computers, and even HVAC, where a lot of guys are pro-Carrier, pro-Trane/American Standard (that would be me right here, even though I work in a Carrier shop, lol), pro-Rheem and so on. The common denominator in HVAC circles is that a lot of people tend to put down Goodman. In my opinion, Goodman has a bad reputation because the company sells to anyone, not just authorized and licensed distributors and dealers/installers, so the so-called "horrible" Goodman products are usually nothing more than the cause a bad install, which is not the fault of Goodman. Are they the best thing out there? No, but given a proper install, they're decent. In my opinion, Trane, Rheem and Carrier (in that order) take the cake on the best units, but then again, it's my opinion and I totally respect the opinions and viewpoints of others (for example, a seasoned veteran feels that Trane/American Standard falls short in its spine-finned condenser design as it could collect and retain things like dryer lint, dog hair, etc., which would be hard to remove) and I have only been on the job for less than four years. Any system will fail much sooner if someone who isn't trained performs the install. HVAC is so granular we even bicker about commercial reach in fridges. I can't stand True reach ins or any of the low-end makes like Turbo Air (I think McCall and Traulsen have a superior design, since everything is at the top and easily accessible), but a lot of guys love them.
Anyway, back to vacuums, I can see why people love Dysons and dislike Kirbys. To be fair, a Kirby is on the heavy side, the attachments take time to set up and AFAIK, I'm not sure that the most expensive Dyson comes close to the price of a brand-new Kirby at full price. I also recognize that Dysons can and do live out reasonably long service lives. My aunt Kim has a Dyson Animal (not sure what model exactly) from 2006 that is still running today and has never seen a service center AFAIK. Likewise, I'm sure there have been a few Kirby vacuums that have burned up in less than two years, even in the hands of a careful owner.