Personally, whilst Which may appear to favour premium vacuum cleaners, I don't think they have always recommended things that people "cannot afford."
HiLO- Bosch has slightly better quality, uses similar Wessel Werk floor heads to both Miele and SEBO. Dependent on model, the dust bags for the smaller BSGL3 series are more in demand also helped by the fact that John Lewis had a similar model under their own name and sells 5 dust bags.
Keith - the D2 that you feel "hasn't done that well," was a previous Which winner...It is bulkier because it has almost twice as much cord length as your Miele S8 and actually, ALL of the Miele cylinder vacs.
However as with the K series, you get almost twice as many dust bags for the amount Miele charge.
Steve - Good luck on the K3. Im not a fan of the K3 Premium. As the owner of the K3, the hose is too bulky, winds on its own and kinks easily because of the embedded electrical cord inside. I've also had problems (as well as others have had) with the pigtail plugs behind the handle to the electric tubes. If you don't like the idea of bending down, you'd have to do it on the K to get the crevice tool out, anyway!
The same crevice tool, longer than most other brands acts as a secondary extension for the Sebo Felix - it isn't a conventional cylinder vac - and I find it a heck of a lot easier to use its upright design plus the longer power cord on it and for the simple fact that it has the more modern ET-1 floor head with brush roll on/off - if you buy the K3 Premium it comes with the simpler, slightly heavier non-manual brush roll stop ET-H in the UK.
At least the Vulcano only has the longer 2.1 metre hose with the controls on the handle. That is slightly better, but the hose is still liable to kink.