I've only had my hair cut at the Aveda 'flagship' in Covent Garden where I had a great stylist. But I think I'm right in saying that most of the Aveda salons around the country are franchises, so probably do their own thing and vary in quality. But others with experience of them will know more about them than I do.
I go the Aveda in Colchester and its nice enough, I wouldn't consider them any different or better than Toni & Guy, though the do try to make a bit of an experience of it by giving you a head massage (if you are having your hair cut) or a hand massage (if you are having a colour done). Not overly cheap but not that costly either.
I had my hair cut at the Aveda 'lifestyle salon' in Westbourne Grove. I'd now run a mile from anything that calls itself a 'lifestyle' anything.
They offered a shoulder massage and head massage and the decor was all biscuity, but my hairdresser kept trying to flog products which really pissed me off! And the bottom line was the cost of the cut was about £75 for what was basically a ponced up trim. And then she said: 'I'd like to see you again in four weeks' with the air of being a medical consultant.
I've had fantastic haircuts at small salons and shit cuts from queeny hairdressers at glossy salons so I'd say the best haircuts are those where you build up a relationship with the hairdresser and he/she knows your hair and its quirks. You should never feel pushed into having a cut you're not comfortable with and just because it's expensive doesn't mean it's going to be worth it.