I was with BT until a few months ago. They upped my bill from £32 a month to £41 with very little notice (a sneaky email in amongst the crapton of marketing emails they usually send). Considering my service couldn't get a connection for about 50% of the time, the 'service improvements' excuse that BT's various drones kept spouting didn't exactly go down well.
I'm with Zen now. Haven't had a single connection issue since the second the service went live. No throttling. And they're charging me £17 a month (to go up to £32 after the first six months). In all fairness, I can't say how good their customer service is. I've had no need to call them.