I used a local company, a family firm, for our new front door and windows. They were courteous, throughout, no hard selling or bullying, from the time the rep came around to the arrangements for fitting. They did a really good job and the after sales service for some slight adjustments was first class, even coming out on a Christmas eve for a minor problem.
They may not of been the cheapest, but they are the best.
They go by the name of Barnet windows unsurprisingly.