Hey, somebody finally pulled me out of my forum lurker status!
Like Melissa I use a Miele Callisto. There are several videos on YouTube comparing particle filtration with Miele versus Dyson vacuums using a particle meter at the exhaust. The results are startling, with the Dyson models usually showing a much higher particle exhaust than the measurement for the air in the room. In other words, it's actually polluting the room. Measuring the Miele exhaust, the particle meter quickly goes down to zero. The main difference (I think) is that the Dysons don't have a good seal around the HEPA filter, so dust can just go around it.
If you have the money to spend, a really nice vacuum may last you 20+ years. I'm not familiar with Riccar or Windsor; those might be good brands, too.