Cost is a huge issue
As an audiophile since I was 13, I understand that the more you go up in cost, you get incremental boosts. I have always prided myself on choosing the best products at various price points and knowing the market to find value items that work well together for less than the TOL products.
I find vacuums similar. It's all about taste and what gadgets you may want. I never cared about bells and whistles on my audio gear. I still run tube amps and preamp on my main system and I use a turntable and vinyl too. It's time to retube and that is costly, but the sound is addictive to anyone who has hear a proper tube set up.
I think in vacuums, that Miele, Lux and Kirby have set the price bar. I chose these three as they are the most known/available high end canisters and uprights. All of their TOL are basically around 1500 give or take. From there you go down in price, but you may loose features or power or build quality and it's up to you to figure out what you can and want to live with.
So many on this forum love Hoovers, Sears or Panasonics. Taking nothing away from them, but they are not in the same league as the Sebo, Lux, Tri STar, Kirby, Rainbow, Miele, Riccar/Sim or any of the other 'high end' models out there. They just aren't, but that doesn't mean they can't clean as good. It depends on how you clean and what you clean. The big difference will be cost over 10 years. That's what I went with when I broke the bank to buy a 700 vacuum. My wife wasn't happy of course as she wanted a nice box store model that she's known from TV ads. I didn't want to go disposable. I wanted some control on the wand handle. I wanted one that would stand up over time and look good in 5 years. I wanted a good filter system. Those were just my wants and I found what I was looking for. I'd change a few things on the D4 if I could, but overall, I'm very very pleased and I like looking at it and using it. That's what counted to me.
George has to have large tools and they much be onboard (I wanted them on board, but didn't care about size as long as they work good and in my home I love the sizes of the onboard tools as they reach the spots I need them too). Some would have wanted the 16" head, but I didn't. I did want white, but took black as that was the demo and the price was right.