Ive been with Sky Fibre for years now. I always seem to have a good connection until recently, but that was due to an external fault which was fixed within 3 days.
Most of these companies rent their lines from BT anyway with the exception to Virgin as they are direct fibre lines.
Most of your connection speed and health will down to the lines and switches in your area, not the ISP you go with.
Something I did find helpful with Sky is that they have a diagnostic tool which can tell if any issues you are having are in your home (From your master socket) or they are on external lines out of you control.
Most of these companies rent their lines from BT anyway with the exception to Virgin as they are direct fibre lines.
Most of your connection speed and health will down to the lines and switches in your area, not the ISP you go with.
Something I did find helpful with Sky is that they have a diagnostic tool which can tell if any issues you are having are in your home (From your master socket) or they are on external lines out of you control.