In my experience you'll likely to get the best service from national companies that have been around 30 years or more. Everest yes are the most pricey but they are the best. Anglian provides good quality products at a fantastic price if you beat them down
I do not trust any company other than Anglian and Everest and while I acknowledge that many might disagree there's no getting away from the reality.
Looks like you found someone who disagrees.
With 20yrs + experience of fitting and repairing PVC i saw some sights and i wouldn't trust any national company and i would never believe anything a double glazing salesman told me.
For the last 15 years i've been a service engineer after gaining all my knowledge working for small local window companies to fairly big regional outfits, i have seen just about every profile their is and seen some of the worst bodges ever, most coming from national companies including the 2 you mention.
National companies promise the earth and rarely deliver, they employ pushy salesman who eat all your biscuits and won't leave until you fold and you just end up signing to get them out the door cos you want to go to bed, they can seemingly knock thousands off their quote at the drop of a hat (or a phone call to their manager
), they all say THEIR profile is the best, they spout off all this bulls**t about a 16 day cooling off period but take 3 weeks to send you the contract that tells you as much, don't ever ever ever ever ever EVER believe anything that comes out of a D/G salesmans mouth, unless its your fist.
I'm currently working for a national repair company, we are sent to look at anything from a shrunk gasket to a whole conservatory or even a house full, again seeing all wonderfull things like brown silicone used to point brick horns with cos they didn't have sand and cement, box gutters that look like they've been welded by a 5 year old, windows fitted upside down and had 7 attempts at re drilling new drainage holes.........oh jesus you got me all started
IMO nationals are best avoided, their customer service will be none exsistant, the fitters are never in the area suprisingly, the girl thats dealing with it is off having a baby blah blah blah blah.......yeah i've heard them all, i've had customers break down in tears in front of me when telling me about the 'National' company they employed, i've had customers telling me about 2 year court cases, i've been in houses when the directors of a certain national company have knocked on the door for the withheld cheque, even heard them say we'll see you in court then and we never lose!!! All from a company that was your best mate when you were signing!
This is only my opinion but i would go for a well known regional company, one that works off reputation not a 50k a week advertising campaign.
Oh and one last thing, never believe anything a double glazing salesman tells you............the chances are he's lying!