In my 10 plus years of experience with Miele, I'd say Miele canisters are just fantastic for general cleaning with. Quiet and efficient they are so easy to use and the spares, attachments and versatile design means you won't go wrong.

However through my years when I discovered that alongside my parents 15 plus year old Sebo X1 Automatic (same as Windsor Sensor) that only required one drive belt replacement in its life, I soon became a fan of the Sebo canisters. They do everything that the Miele vacuums do from my first statement - BUT the Sebo canisters also last longer, have better plastics, don't show up scrapes as easily, have lighter tubes, cheaper dust bag costs (based on the fact you get twice or more than Miele's default 4 in a box) the D series has a bigger dust bag and almost twice as much mains cord length on offer. Power wise without PN nozzles, I've never seen a difference between Sebo and Miele vacuums, but design wise I much prefer Sebo - I wish sometimes their models had the same kind of oozing touch feel goodness that Miele canisters reek of - but I'm glad the main controls on the top don't have a breezy exhaust that puts out hot air, no matter how "clean" Miele claim it is with the AAC or HEPA filter cartridge fitted. I'm not sure as to why a Miele S6 has been shown with the D series next to it as the D's natural rival is the similarly sized S5.

From a visual point of view, Miele wins - they know how to dress up a vacuum pretty well in terms of silver inserts, flashing lights and so forth.

Sebo are more the conservative company and build highly efficient vacuums with simpler controls, and sometimes unique features for a simpler life. (The AirBelt is fantastic for protecting both the home and the machine on the canisters.)

As FantomLightning suggests, do a trial of both products. I also have an S5 myself - it falls over from time to time like most cylinder/canister vacs and the D series is only slightly bigger. The S5 also has a very short power cord - an extension cord is not a safe option in my opinion - I like vacuums that have everything on board, not something else I have to carry around with me to get extra stretch and buying an extension hose to go on the back of the handle that Miele also sell as an additional accessory only meets the travel requirement half way - the hose has coils in it, isn't as long lasting and is inclined to snap back too readily even when full suction is used and liable to swing when fully stretched out, whacking off doors. SEBO offer longer hoses that can be handled with one hand and the main handle instead, minimising damage to the home, and in the D's case, a lot more mains power cord to take advantage of rather than constantly pulling the vacuum along with me as I travel along. 

ALSO - the K series is about the same size as both the S2 and S4/S6. Therefore it would be a smaller machine with a smaller dust bag on board. Dependent on the size of the home and the cleaning needs at the time, K series vacs have, again longer mains cord and still more dust bags and longer lasting filters than Miele offer with their FJM series. The winning card that Miele offer with their S2 is the bigger GN S5 dust bag and I'm sure the U.S have models with PN nozzles built on. I suspect then that the consideration then will be Miele based on the fact that consumables are more readily available compared to the recently introduced K3 or K3 Vulcano in the U.S

Well the tools have improved on the D series. The K series uses a smaller version of the larger dusting brush that came with the Sebo C. Mind you, I like the round dusting brush on Miele vacs - they're better now that they have proper long bristles compared to the castle cut style that was liable to clog up too quickly. I, too find that the crevice tool on the Miele is too noisy - the long one that comes as standard with the Miele Vario Car Clean kit is much quieter.

This issue of tools brings me onto another subject - I've recently bought two new tools for use with my Miele vacs, the long dusting brush (SUB20) which is really good and the mini "mini" turbo brush that looked quite good at the time. 

As Ive said before, Miele are a big franchise company, churning out all manner of household appliances as well as holding a great foothold of medical cleaning machines for the health industry. They don't however produce commercial vacuums. That's where Sebo come in AND in the UK, Miele are better known - so its not as if Sebo are any different in the minds of most buyers. Which UK recently put Sebo as their number 1 brand for reliability of uprights and Miele as number 1 brand for cylinder/canisters. Ironically enough Which's excuse for either was that they didn't have enough data for Sebo's cylinder/canisters or Miele's uprights.

How long have Windsor been churning out the Sensor models in the U.S? Sebo came to the UK in the 1990s and they have been going since the early 1970's. I suggest however that you learn a bit more about Sebo and their brand - as a private company they merge with lots of sub-contract cleaning companies to put their machines into the industry and really, if Sebo weren't going to last in the U.S I doubt they would have allowed the U.S arm to heavily promote the machines through the use of videos. Even other countries are using the U.S videos that Sebo U.S have created. That doesn't suggest to me Sebo will be a short term stay in the U.S!

End of the day though, it's not about how popular a brand is when it comes to certain appliances - its about how they are made and how they function - and the original poster that created this thread is initially confused as to which brand to go for based on their cleaning requirements.

Here's a question that I'd like to know the answer to.. given that Miele have several different PN's available - are all the brush rolls the same? Or does one particular model have stiffer bristles? Do any of the PN's have a brush stop function like the Sebo ET-1 floor heads do?

Ah. You see I'm not a fan of canisters with PN's. I have a K3 Premium myself. I find it too bulky and the idea of saddling a compact, lightweight vacuum with a PN isn't my cup of tea. 

Many years ago I did try a Miele S500 (not sure of the number) Revolution which had a powered nozzle head in the UK. Far too heavy and compromising. The K3 is smaller and much easier to handle WITHOUT the PN added, lol.  

At least with the Sebo ET-1 which the U.S is lucky to get as the UK models get the older, original non-lock ET-H on the K models, you can change brush rolls from the standard blue tipped bristles to a softer brush roll for softer carpets/delicates - uses the same brush roll as the X/Windsor.