I decided to change internet provider when I moved house.
Good: I called a http://fast.co.uk/ based on some good reviews and the sales guy was an absolute delight to deal with. He explained things very well, took his time, and was very respectful. I hope they keep this up. I'll be recommending them to all my friends.
Bad: I'm currently with a crowd called biscit internet who - when I emailed to ask for a refund when because I'd paid them twice each month for the last year, rather than the more common once - discovered that according to their accounting system I "owed" hundreds of pounds for fees which they couldn't explain, apart from that their accounting system said I owed them. I would have happily paid them if they could have explained why. I always pay my bills. But now, after 3 years of adequate supply, they lose me and my money, and they get me saying aweful things about them on the internet.