I would always recommend BT. BT still provide nearly all telephone lines in Britain today. Even if you go with some broadband provider that nobody has ever heard of, the physical line will still be provided by BT.
Even if you have your Broadband connection with the Fluffy Bunny Internet Company, you will still need to pay for a BT telephone line.
Don't get confused by all the vans driving around with "Openreach" on the side...its still BT whatever this weeks name has been changed to !
I have had a BT line for nearly 40 years and an internet connection since 1994. I have always found them to be reliable.
The cheapest isn't always the best.