I'm on Plusnet premier option one. I'm reasonably happy with it, although the service seems to have degraded a little during the last couple of months. They also have some bandwidth throttling issues for some applications, ie peer to peer is very slow during the day, but is a lot faster at night - that kind of thing...they also throttle back your bandwidth as you approach your limits (20gb peak time for option one, unlimited off peak. Peak is 4pm to midnight)
All told though, I've been with Plusnet for about 2 years, and i'm not in a huge rush to change.