I've had both. I prefer canisters because they're easier to maneuver and the ones I've had are more versatile than uprights. I have mainly hardwoods with area rugs with some carpet. I have a small house so like a smaller unit with narrower path.

CR says "How to choose

Start by matching the type to your cleaning. Uprights, especially with a bag, do best overall on carpets. Canisters are easier to maneuver, particularly on stairs. Here's what else to consider before you buy:

Check the features. A brush on/off switch helps protect bare floors and avoid scattered debris. A motorized brush cleans carpets better than only suction. Also helpful: manual pile-height adjustment, which can be matched to carpets better than with automatic, and suction control for cleaning delicate fabrics with tools.

Consider bagless carefully. Bagless vacuums save on the cost of bags but still require filters. And the dust and mess of emptying their bins is a concern if you have asthma or allergies.

UPRIGHTS:
Pros:
Uprights generally provide a wider cleaning swath than canisters, and they tend to be better at deep-cleaning carpets. Most are also easier to store.

Cons:
You must drag the entire machine back and forth for most floor and carpet cleaning. Some top performers weigh 20 pounds or more, although many competent machines are much lighter. Uprights also tend to be noisier than canisters overall.

Know about the noise. The noisiest vacuums we tested produced 85 decibels or more, the level at which we recommend hearing protection. Canister vacuums as a group tend to be quieter."

CANISTERS:

Pros:
Canisters tend to be better than uprights for cleaning bare floors, drapes, upholstery, and under furniture, and they're easier to handle on stairs. Most are quieter, and you mostly need to move only the hose and powerhead, not the entire machine.
Cons:
The entire vacuum tends to be heavier and bulkier than an upright, and the hose and wand make a canister harder to store.
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I have an expensive Miele canister, so it's lightweight and does an excellent job on carpets, as well on hard surfaces. I can flatten the wand to go completely under the bed, and it's a snap to change accessories. I find ability to change level of the powerhead AND level of the suction is very helpful. It rolls easily and is easy to push the hose with powerbrush, compared to the uprights I've had.

It's also true that canisters are more of a bear to store because of that loose hose, though.

Uprights are definitely less expensive.

As for dust and allergies, I think that would depend on whether you get one with a filter or HEPA filter, not whether it's an upright or canister.

Hmm, that's weird.

I'd also read Consumer Reports, but I must have missed the part that said uprights " tend to be better at deep-cleaning carpets."

Instead, when I read CR, it kind of muddled the issue about which cleaned carpets better.

CR said,"Nearly all canisters do a fine job of cleaning bare floors and on stairs, but carpets remain their toughest challenge. Top-scoring models combine impressive deep-cleaning with strong airflow through the hose for use with tools for cleaning upholstery and drapes. "

And, then, it also said, "Nearly all full-sized uprights cleaned bare floors quickly and neatly, but carpets remain the toughest challenge for most machines. Top-scoring models deep-cleaned impressively while providing strong airflow through the hose for use with tools."

http://www.consumerreports.org/cro/vacuum-cleaners.htm

So, it sounded like to me that CR was saying that both canisters and uprights had trouble with carpets but those two types could still deep clean carpets without saying one was better than the other.

Oh boy, another vi-vs-emacs issue (b.t.w., vi wins).

[flame-proof suit is on]

IMNSHO, canisters tend to have better overall performance in most categories but price (for decent quality, and most likely in US; uprights are not popular in most places outside US).

Beside the maneuverability advantage, the airflow in a canister has fewer direction changes, which improves the suction ability.

[flame-proof suit is off]

As usual, many times it's a matter of tradition and personal preference .

"I'd also read Consumer Reports, but I must have missed the part that said uprights " tend to be better at deep-cleaning carpets." "

Forget the article itself. One has to look at the ratings charts of both canister and upright vacuums, at CR magazine. Look at how they perform in the carpet category. There is where one sees the difference.

Regarding Consumer Reports.....what I posted was a quote, which I should have indicated. So CR says uprights generally are better at carpets. I don't know why they say that. There are exceptions to everything, though.

I like canisters for several reasons. But that's me and my types of flooring and house size. I just have two small rooms with carpet.

One thing I DO know: it's not necessary to spend a lot on a vacuum cleaner. You can (I did), but it is not necessary. It's easy to get carried away with buying better and better and best for more and more money. It's not always true you get what you pay for. You can spend a lot and get just average. Look at customer reviews for what you need (for example, I need pet hair pickup on carpets and area rugs....anything will pick up pet hair on hard surfaces, frankly), but you may have other needs. And look @ CR ratings.

[QUOTE]the airflow in a canister has fewer direction changes, which improves the suction ability. [/QUOTE]

If that's true, then why is the conventional wisdom that uprights are better at deep cleaning carpets if a canister has better suction?

And, I don't really understand how the airflow in a canister has fewer direction changes. Could you please clarify/explain that in more detail.

I'm a bit clumsy, so I find the hose and canister a bit unwieldy. We had one growing up. It cleaned fine, but I can't comment on carpet as we had very little.

I recently purchased an upright Riccar after much research here and elsewhere. It was in the same price range as Dyson, but made in the US (which wasn't a primary concern, but a nice bonus) and has sturdier construction. It is fantastic. We have both carpet and non carpet areas and it does a good job on both. The carpet actuall looks and feels better after vacuuming, I was shocked.

This issue is clouded by the fact that all vacuums tend to now be throw-aways that compete on price. Once it was clear who was the winner in each category. If you can get a good upright it will have a powerful brush rubbing and vibrating the fibers of a carpet while a good (not great) vacuum sucks up the dirt that is loosened. Canisters had very powerful vacuum power to collect as much dust as ome could loosen with the equipped attachments. Simple as that. Now Consumer Reports is contending with both the inherent properties of various models and the junk that is out there. Wwe have a whole house of carpets to contend with. So my wife has a Kirby that does the job. Not junk and very expensibe. It will never make a Consumer Reports best buy category, but it works like all good vacuums did in the old days. I have a small plug in hand held vac. that Consumer Reports said was very good and I use it for all small jubs around the house and cars. Hope you find what you are looking for.

What's more importance for a vacuum, the brush to rub and vibrate the carpet or the suction power of the vacuum?

Maybe, I'm overthinking this, but can the brush be too powerful and end up reducing the lifespan of the carpet? I'm thinking of how life when you use bleach to wash white clothes, it makes them whiter but also kinda shortens the lifespan of the clothes if you use too much.

We've been considering a canister (as opposed to trying to retrofit for a central vac) and I've really noticed most stores don't even sell canisters. There can be 20 different model uprights on the self, and not one canister.

We would want one with a powered head, large capacity bagless, and hopefully a long hose.

". . . but can the brush be too powerful and end up reducing the lifespan of the carpet?"

Possibly, but dirt that has not been removed from carpet will also shorten the lifespan. Seriously, I doubt the brush could be too powerful. Most likely, the vacuum companies wouldn't want people complaining about carpet damage.

Of Consumer Report tests over decades, only a very few canisters were able to clean the fibers of a carpet as well as the better uprights. All those were equipped with brushes that rubbed and vibrated the fibers just like an upright. Suction alone didn't do it. If you can go to the library and find old buyers guides from 20-30 years ago, you can read about that stuff. As I said previously, things are different now. Go to a site where owners can review their experience with modern vacuums (like Amazon.com) and you will read horror story after horror story. I don't know if any vacuums below about $1000 are any good.
Good luck/