Telewest if you are lucky enough to be in their area.
If not Telewest, then Pipex is next in line by repute on this forum. Only snag is that it has just changed hands. To me there's the risk the new owners will try too quickly to recoup the millions they spent.
Ratio capital/No.customers is highish, but may be offset that Pipex have a larger business/domestic proportion; also business may be the less tolerant of poor service.
Unfortunately my Tiscali at present is beyond the pale.