We have gone with a combination of velfac and velux for our windows and doors (now owned by the same company ...on recommendation of the architect. Should be in within a month so can comment further when installed.
We have gone for velfac at the front based on having them in a rented flat. Very happy with them and they look great. Now we are getting the whole back of the house done. My suggestions if you're getting them is ask for a discount as the first price is inflated. Also triple glazing is only about 15% extra if you need it. And look carefully at all the options for handles and fittings, as we added extra security fittings so we can leave them open when we're not in the room.