I just went through this myself. Again. For like the 8th time in 10 years. Stay away from Kenmores - I had a $500 canister kenmore progressive direct drive that had to have $100(+) worth of repairs EVERY YEAR. I did ALOT of research and came down to:
Dyson - which was too costly to repair as parts are imported and typical repairs took 3 months to receive parts, also heard from alot of owners including my DH's best friend a complete clean freak that they're great for a year then lose suction - DH's friend's wont even pick lint off the top of the carpet now,
Kirby - both of our mothers have 40/yo Kirbys but all the sales guys said that the new ones are lucky to last 5 years AND they were too tall for me, extremely heavy, and not practical with our stairs,
and the Miele Capricorn which is what I ended up getting.
I love my Miele. I've had it for three months now, still haven't had to change the self-enclosed bag due to their unique technology. It's the only vac the allergy/asthma sites all recommend (and we LOVE it for that - incredible filter!). It's the quietest, smallest, lightest vacuum I've ever had. Consumer Reports LOVED it and gave it very high ratings, tho they don't recommend them due to the price. and typically they last 20-30 years. It's the BMW of vacuums and you pay for it, but you won't be putting $100+ every year into a new vacuum or repairs. It's german engineering. It's incredible. But, a vacuum is also a very personal thing. It was the right decision for our family. I probably won't ever go back to anything else. ever.
http://www.allergybuyersclubshopping.com/miele-capricorn-...
If you're interested, here's an allergy website with a pic and some info. I got mine at a local Miele dealer so I acutally got a better deal, tho they never go on sale. I got mine for $30 less than the price on the website + 4 boxes of bags (said 2 years worth, but given that I havent changed a bag YET, prolly more like 4 or 5....)
also, here's a link to my vacuum inquiry a coupla months ago in case that helps
http://www.mamasource.com/request/16733233881527943169
Good luck!