Switched recently from Plusnet to SSE.
Previously (2yr ago) I stayed with PN during a house move. They royally fucked it up and I was without service for 6 weeks. They offered vapourware refunds and refused to let me raise a complaint. I ran out of energy to continue the process since I was dealing with some other big personal issues at the time.
Shifted to SSE the other month who were offering (after cashback) 35Mb fibre and phone for £15 a month less than PN offered to keep me. They also switched me over on the day with less than 1hr of downtime and it's a one month rolling contract so if they are shit I can switch again without much delay.