My fiance sold high end vacuum cleaners for about 2 and a half years, she just stopped selling them about a year ago and this is what she had to say along with some of my input from the vacuums I've used (which are nearly all of them considering every time she sold a vacuum we got a trade in from them to use).
Vacuums we've owned and used
Dyson--My mother, who we're staying with now due to the hurricane, owns one. It is a huge waste of money. The tools are so hard to use, the suction is about average, but the accesories and floor brush pick nothing up. It's a piece of junk IMO
and my fiance's, however, some people love them. I tend to think it's because they can't bear to realize they spent $400+ on a piece of junk.
Hoover, Eureka, Bissel, Etc. Upright vacs---They are cheap for a reason. They do pretty well for the first few months, maybe even to 6 months and they are very convenient, especially bagless ones. However, They clog up and lose nearly all of their suction after about 6 months of usage. I cannot tell you how many of these were traded in. They become nearly worthless after a year, you might as well just sweep your carpets with a broom.
Kenmore canister vacuum--Great vacuum. Really good. I think the most popular model is the Kenmore Progressive 25615, around $300. They always have good suction and last forever. My grandparents have owned one I know that lasted 15 years. If I were to buy a vacuum right now it would probably be this one due to best value for your money and that's also what my fiance said. The accessories work well and the rotating brush is very good at picking up hair--very important with cats and dogs. I won't vouch for the upright model though because I've never used one. My fiance says that canister vacs always have the best cleaning power and suction so you probably lose a little if you go the upright mode.
Miracle Mate--What my fiance sold. The most impressive vacuum I ever used, however it cost $1500-$2500, thus it's probably only for someone with alot of money to use on a vac. The brush is great at picking up hair and the cleaning power is better than anything I've ever used--Kenmore was 2nd. If you can somehow pick one up cheap I would recommend it but otherwise I wouldn't go for this.
Rainbow--Imagine lugging 32 pounds of water behind you when you vaccum. Now imagine you paid $2000-$4000 for it. The worst vacuum ever, it picks up nothing and the usage of water as a filtering device means You actually spread more stuff into the air that will aggrevate your allergies than you pick up. Used it once, huge PITA, and sold it on ebay for $500.
Kirby and Royal--Kirby's are $2000-$4000 and definitely not worth it. They do last quite awhile but they just aren't very good at doing they're job when compared to a Royal which still costs a pretty penny $400-$500 for the good models and are a better machine than a Kirby. Royals tend to last a long while, growing up we had one for a good ten years, but the cleaning power isn't what you would get with the better canister vacs.
Vacuums I hear alot about but have never used
Miele--Best reviewed vacuums and everyone raves about them, however, the cheapest model that comes with a floor brush for carpets is $800. So that's a drawback. I would say that even though we got traded in vaccums like rainbows, Kirby's, tristar's , and others that cost more, nobody would ever part with a miele or Bosche, which is another highly rated vacuum.
My advice is buy the Kenmore canister vac. It's not quite as convenient as those uprights and not as trendy as those new dysons but it is definitely better.