I've always preferred tank vacuums over uprights simply becasue with a tank vacuum you can clean a wide variety of surfaces above the floor. With an upright, you are limited to their specialty of cleaning carpeted floors....a job which they actually do better than tanks though. So, which tank do I prefer? I like the Electrolux and Tri-star (Compact) vacuums the best. They are built incredibly well, and will last generations. They also come with all sorts of neat attachments for just about any job. When it does come to uprights, I like the Kirbys because they possess the same good build quality. Another thing I like in a vaccum is the bag before fan configuration. This keeps solid objects from damaging the impeller inside the vacuum because they are filtered out first. This is one disadvantage of a Kirby...luckily, changing the impellers on those isn't too hard.
Really though, cleaning effectiveness is affected by moving lots of air, not pressure. This is what is rarely advertised by vacuum manufacturers (rarely do you see a CFM rating on a vacuum cleaner!) any vacuum that moves lots of air will do a good job, no matter how much power it uses, or how much negative pressure it can generate. This is an area that I think the Oreck vacuums fall short on. They create a lot of pressure, but don't really move a tremendous amount of air.
The second half of cleaning effectiveness is good filtration. I've rarely seen a bagless vacuum that really filters all that good. The ones that do still have parts that need to be regularly changed, so what's the diff between that and a bag? This is one area the Orecks are good at, and so are the Tri-Stars too!
Another important thing to keep in mind is parts avaialbility. The cheap "fad" vacuums that are sold at most of the big box stores will probably not last very long, but that's not a bad thing, since these important parts like bags, belts and such will probably be discontinued rather quickly. This is one of the ways the manufacturers "purge" the field of old machines that escaped their engineered in planned obselecence. (also done quite heavily in the electronics industry)
