I was Liberty at first years back, then Line One, then Pipex - which was excellent - and when they ceased that service, I was landed onto TT, which was terrible, but I didn't know how terrible until I read a lot more here, and then moved to Zen in 2011.
They put in a new outside cable and master socket, and it was great.
The Olympics mucked it up a bit as I was moved from the Westminster route, and although it's OK now, it's not quite as rock solid as it was then. My location on Google is shown as W10 near Ladbroke Grove since then.
For some reason though, my speed went up a bit a month or so ago after it dropped the connection, and then Zen tinkered with something.(ADSL2)
I certainly wouldn't want to go back to basic TT bb.