Beware of what service you're actually buying.
Virgin (if in a Virgin area), offer fibre broadband. You'll get a much higher speed but may pay a little more. Normally includes a phone line I think? I think they only offer services over their own network, so you have to be in their catchment area.
FTTP (fibre to the premises, anything from 150mbps to 1gbps+, I.e. fibre run right to your house) is getting more common, have a search round. You may be restricted to one company for a little bit til they sort out the sharing/leasing details, but the start prices seem pretty competitive. You will almost certainly lose your phone number unless you transfer this to a VOIP company (or continue paying your line rental to someone for your phone line). This isn't a concern if you don't use your landline.
If getting FTTC (up to approx 80mbps) - the line is generally leased from Openreach (regardless of which provider you go with), therefore the MAX speed you can ever possibly get will be the same for all providers. The individual companies switches/infrastructure/packages then limit your speeds further... I pay £21 per month for TalkTalk 80mbps FTTC, and have done for the past 18 months, with £20 per month for the 18 months before that. Expect this will rise to like £24-25 on the next bill due to CPI increases. TalkTalks customer service can be very hit or miss, but the service I've had has been nothing but perfect, and when I reach the end of contract I just ring up (ignoring the "deals" they send) and say I'm leaving, and they match, or close as damnit match the other price. Last contract end deal was £27.99 per month, and they dropped it to £21pm to match Vodafone. If you have speed problems with your current broadband caused by a line fault, this may transfer to any other provider that you go to.
Finally, some companies still offer plain ADSL2+, normally at the same cost as the basic FTTC packages, but there is absolutely no reason to get this unless you don't have any option for FTTC.