Broadband providers outside of mainland Britain

Residents of the Isle of Wight, the Channel Islands, Isle of Man and everyone living off of mainland Britain, how does your broadband compare to the mainland?

I was recently reading that Islanders in the Outer Hebrides have come together to create their own superfast broadband network and it got me wondering if broadband connections differ massively compared to the mainland? Is the infrastructure still Openreach or is it independent, who are the best providers and what speeds can you get?