Which Brand is best and why?

Elephant
Esure
Admiral
Diamond
Sheila's Wheels
Direct Line
Confused.com
Norwich Union
The AA
More Than
Swift Cover
Norwich Union are the dearest insurers. They are rubbish
I use Provident. They gave me windscreen cover on TFT
Bonus
Also some of those above only deal insurance for women
Confused.com does a large search on all of the above and more
I cannot tell you which is best due to the fact that it depends on exactly what you are looking for. However, I can tell you that Esure and Sheila's Wheels are one and the same. Though the Sheilas Wheels policy has a few more perks on it like £300 handbag cover which you would not get on regular policies from any other company.

Norwich Union and More than are again the same company I believe and generally feedback I have heard from them is quite poor there service is not up to much.

Direct Line is a reasonable product though if you are involved in an accident they do not provide a free courtesy car but a hire car which you would be expected to pay a collision damage fee for if you had to use them.

Diamond and Elephant are both part of the admiral group also, but they seem to be quite good too.

I would avoid companies like Swiftcover, although it sounds good in practice having no call centres etc there is only so much a computer can do and if you have a complex issue it may be best to be able to speak to someone directly who can sort it out for you rather than say we did not receive your email.

I do not know much about the other companies but my advise to you would be to check on their websites and read through the policy booklets, it is very boring but it lets you know exactly where you stand.

Personally I would go with Shielas' Wheels despite the annoying adverts it is a good policy.
The best "BRAND" is Direct Line as they probably have the biggest market share of insurance clients and are the most well known out of all that you mention (in the UK).

NU are a very close second but that wasn't part of your question!
Penguin

Answers:

Defo Priviledge.com always been the cheapest for me!
Dont touch Norwich Union.. They quoted me un happy
elephant i was quoted £900 on a 2.5 litre focus st an that is cheeeeeeeeeeeeeeeeeep when im only 23.....
None of them!
elphant...cos its on the top
what are these brands for ?
I guess this is for insurance? Admiral are excellent for mid-20's males with a good driving record and a group 20 car (ie me), diamond are also very good for this strangely enough. Shelias wheels are good for nobody, but profit out of daft blondes with pink seat covers and pink dice that just like the advert and the name. Dunno about the rest or other situations!! Wouldn't cover my girlfriend with a 1.5 Hyaundi Coupe MVI because it was a coupe, and even wanted £562 for a friend who was 21, had 3yrs no claims and insured a 700cc Fiat Chinquecento, also known as a pepper grinder! Tesco offered that for £170