The trust, which allows members to visit its 300 sites for £46 a year, topped the list, chosen from the 500 charities featured on Intelligent Giving's advice website. Welsh National Opera was second, followed by English Heritage, the Tate galleries and the Centre for Alternative Technology in Wales.
A special mention was given to the Royal Opera House, whose £44,000 annual membership scheme for patrons includes meetings with opera stars, priority access to the royal box and the opportunity to use private dining rooms.
Members who pay more than £35,700 can secure the right to guarantee their favourite seats at every performance.
Researchers from Intelligent Giving advise opera buffs on a budget to go to Cardiff, where supporters of Welsh National Opera are offered the chance to schmooze with musicians for a mere £35 a year.