BT Fibre & EE mobile
Worth pointing out that both are on business contracts.
May be a case of getting what you pay for because so far I've had excellent service from both of them.
Previously I was with O2 for mobile (also business) but post-iPhone introduction into the UK the service offered just kept being cut down ever more. Used to be, for example, if there was a problem with the handset they replaced it next working day. Ok the replacement would be a refurb unit but still..next working day. New one delivered, hand yours over sans battery, sim and accessories and carry on.
BE Unlimited were my ISP of choice - again on a business contract. Never had a single issue except they didn't do fibre, hence moved to BT (at the time I placed the order the day it became available in my area and they were the only provider). Only had a few issues early on and they handled them well, and quickly.
I was nervous of going to EE at first - I'd heard and read bad things about their consumer services but they were winning awards for their business services so I decided to take the chance. 50% less cost than O2 and went from 1GB of data to 36GB.
Three - had a one plan sim for using on their all you can eat tethering. Great when you get a signal but again, their customer service was lamentable.
Vodafone were just too expensive for everything.
Ayway...EE and BT so far for me have been absolutely fine. YMMV