I've been online since my 90's days with Pipex and Demon and in all that time, on various ISP's PlusNet have been by far the best.
Not only for their network performance, but mainly for their support.
They actually employ support techs who know what the heck they are talking about.
Since the 90's, I've only used Pipex, Demon Internet, Pipex -> Tiscali / Talk Talk and BT so my experience with others has been limited. (I did have 3 years in Texas back in 1999 on a 20meg up/down cable connection only to come back to the UK in 2002 to drop down to a 300k/500k up/down connection with Pipex which was a shock).
My father also switched over to PlusNet and they've been great with getting his line sorted out without the need for me to get involved.
I had heard scary stories about the PlusNet Thompson router, but having now been on PlusNet FTTC for the past 3-4 months, it's actually been one of the better routers I've used (and I've a stack of them sat on my shelves in the garage).
I don't use the wireless in anger as I have most of my machines hooked up via wired ethernet, switches in various rooms and wireless repeaters all over the place. The Thompson may not be the fastest, but it's the only router I've had in years that doesn't roll over at the drop of a hat and I have 3 kids who are constantly streaming media all over the house and I work from home (200-300GB a month).
Of course... YMMV but for the support alone, I will always recommend PlusNet.
They day they change their support and I have to use some 'overseas' script follower without a clue will be the day I think about leaving them, but until then, PlusNet all the way...