It's a difficult one this. On a purely price level, I'd say B - but at the same time I don't believe unprofessional retailers who provide poor customer service deserve to be rewarded for it by giving them repeat business.
However, if I was buying a big ticket item with a substantial retail mark-up, which bikes and accessories have, I'd expect at least a token sweetener discount in return for A getting my business rather than shop B. After all, £50 off a £1k bike isn't going to kill them, and it's another sale all said and done.
The discounts being offered off bike fits, clothing, and gear are no good if you don't actually want a bike fit, clothing, or gear. I'd sooner have a few notes knocked off the bike itself. It reminds me of the old trick used in the motor trade where bits like extra mats and mudflaps etc would be throw in, but the dealer was still reluctant to discount the car price from RRP.
Given the choice of a good dealer who wants to charge full price and only offer discounts on extras I might not want, or a crap dealer who is cheap, but I would begrudge giving them a penny, I'd probably look for an option C, which might involve buying the same thing either online, or buying secondhand way cheaper than either A or B.