EFT is the way to go with Adsense.
Most UK banks will charge a commission fee of around 2.75% to convert your USD checks into Sterling. This is quite frustrating because the charge obviously increases as your commission checks increase. But when you work it out, 2.75% is a pretty small amount to lose if you're dealing with thousands of dollars.
EFT conversion fee is definitely lower than 2.75%.
PayPal currency conversion fee is at 2.5% so a little better.
Also be warned, conversion charges work the other way as well, so if you're paying for advertising in the US using a UK credit card, you'll be charged 2.75% for the conversion again. This is avoidable if you find a credit card that doesn't charge for currency conversion.
Unfortunately, converting foreign currency to Sterling doesn't seem to come without a conversion fee, no matter who you bank with.