Hi J.,
I'll offer my 2 cents here, since I haven't seen anyone talk about this yet. I have been a professional house cleaner for a number of years and have used A LOT of different vacuum's in other people's homes. Here are some of my tried and true tips, for what it's worth:
1. If you use a bagless vac, you have to empty the canister after every use or you lose suction.
2. Any kind of vacuum will get clogged if you vacuum up things that shouldn't be vacuumed. Pick up the big chunks first.
3. Any vacuum with "on board" attachemets will not have good suction. If you have a vacuum pulling stuff out of the carpet and from a hose at the same time, both places lose suction. Your best choice is a vacuum that requires you to remove the head and beater bar and replace it with a hose. You will have optimal suction that way.
4. Vacuums with bags are not bad, just be sure your connections are secure and spend the money on name brand bags and ones that are designed for homes with pets. The bags are a bit different if you want ones that will contain pet dander, it's worth the money.
5. You get what you pay for. Yes, a quality vacuum can be expensive, but you will buy one vacuum, it will last you 20 years vs. a $200 Sears model that will last a year or so.
6. Have your vacuum serviced on a regular schedule. Keeping up with maintainance is must, your vacuum will last longer and you will get a better clean.
I have used an Oreck, they are lightweight, and professional grade. It will last. I have not used the Miele brand, so I cannot offer anything there. Dyson is popular, I have mixed feelings on those, but would not buy one.
My personal choice is Kirby. I own a Kirby and have used it for my own house as well as houses I clean for more than 11 years. They are heave, and yes, I paid a pretty penny for it, I have all the hoses and attachments, including the carpet cleaning system. I have spent just under $300 total in almost 12 years for service, maintainance and parts/labor costs. I have no regrets, it will last for 25 years, and then I can have to motor rebuild and use it for another 25 years.
When we moved into a new house, I had the carpets cleaned professionally. From that point on, I have done it myself with my Kirby, I have not paid for carpet cleaning since August of 1998.
I'm not a Kirby salesman, nor do I send the sales guys calling on my friends, but if someone asks, I highly recommend the product. If you have the chance to have a Kirby rep come into your home and do a demo, take them up on it. See what it can do, then go find a vacuum store and see if you can buy one used. Or look online/e-bay/Craigslist, etc. and find one used. Check with the Kirby store nearest you for used models. There are people who choose to upgrade to a newer model every few years or so and trade in the older model. (I don't know why, they last forever,) You save several hundred dollars that way, and you will not regret the decision.
Good luck!
G.