Builder A - Long established (50 plus years) family firm. Have lots of accreditation - federation if master builders etc. Recommended by a friend for whom they did some work recently. The guy who came out was very friendly, professional and gave a very reassuring impression of their service and capabilities to deal with the job efficiently. The quote is reasonably detailed but there are a couple of changes/details to be confirmed e.g. Haven't had a site visit by plumber or electrician to confirm minutiae of exact requirements.
Builder B - one man band type company. Came across as friendly and thorough in his approach. Clearly doesn't have the same history of experience/reputation as the other. However, has been very detailed in his quote e.g. sent plumber, electrician round etc first. I suspect the service will feel much more 'personal'. However, no recommendation from anyone I know.
After A left I felt really confident and impressed. After B left I thought 'let's see what he come back with', but have been impressed with his communication/detail since. Wwyd?
I think that I would actually be worried about him sending a plumber and electrician to have a look at the job - it would make me think that he has limited understanding of things to need to send people over. If you like the look of him, ask him to put you in touch with a former client or two and speak to them.
Think I'd go with B as he'd likely be the one doing the bulk of the work / on-site whereas with A it sounds like he'd be "overseeing" the work. Sounds like B has a reputation to build as well so will want to see this job go well / get a good write-up. Our B was fab, but have several friends who have gone with A.
See if you can speak to some satisfied local customers, or at least the ones they are working at now. As for the website, I know a person who does astoundingly neat and detailed work, and shows us photos of it. He put them on his website, and finds copies on other people's, passed off as their own.
BTW (too late now) a useful trick, when you drive around your local area, is to keep a note of any building work you see going on, and ask for a card. Write the house address on the back. Afterwards, you can ask the householder's opinion. Builders and tradesmen are often pleased to be asked, and so are householders.