Depends where you live, how upgraded your local exchange is and whether or not you have cable access. There is no short answer to the question.
Most people in this area think BT is shite, we cannot get any cable network because there is no cable available and the exchange is not due to be "unbundled" for another two years so "Talk Talk" is also ruled out.
Personally I use "Utilities Warehouse" which gives me reasonable speeds (but then I live within 500 metres of the exchange) and includes telephone line rental and gives me free telephone calls to any UK landline at any time. Total cost for landline (includes call waiting/answerphone and a second incoming number), broadband (unlimited downloads) and calls to UK landlines 24/7 = £37.50 per month which is the best value I can find anywhere.