Always check what percentage of the charity's turnover is dedicated to "admin" costs e.g. via Charity Choice website. I donate monthly to various different charities but they are all very small ones with no highly paid CEOs, and where the majority of the workers are volunteers. I must admit I tend to avoid the larger ones like Oxfam as they spend a huge amount on unwanted advertising material but I admit I do use their charity shop, both to buy and donate stuff.