If you looking to undertake a balance transfer for a short period of time, this new deal is the best in the market.
Barclaycard are offering 0% balance transfer for 6 months with the lowest fee of only 0.25% (a fee of 1% will be applied and then reduced to 0.25% by a refund). So on a balance transfer of £4,000 you will only pay £10.
If you are looking for a longer balance transfer choose their long term BT duration e.g. 0% for 33 months although the fee is higher. Will add links in comments.