The reason I always hated Dyson's were, sure their suction didn't reduce over time, but best case scenario, a normal hoover with an empty bag had a LOT more suction to start with, as long as you empty the bag regularly a normal hoover always had far higher suction than a Dyson. I don't know if thats changed, my parents Dyson other than breaking down fairly frequently, still suffers from the inability to pick up a huge amount of dust because its just weak ass crap.
Miele isn't a tough call, with almost any household appliance a Miele = no problems, 20 years life with very little trouble. Expensive to start off, but MORE than worth the extra with the lack of problems you will have over the years and the amount of time a Miele anything will last. Looking to pick up a Miele dishwasher when the new models are all out in a month as talking to Miele direct, they said everywhere should have sales on as they want to ditch the old models.