Hi Lil,
I work for one of the main breast cancer charities (I won't say which one for fear of bias) but outline what each does:
Sadness, mentions Breast Cancer Care, so I'll start with them. Care are about just that, giving support to patients and their families through advice, counsellors and support groups.
Then there is Breakthrough Breast Cancer. Breakthrough have two main areas, research and education/campaigning. Their research centre has recently developed what hopes is a wonder drug, the PARP inhibitor (I am sure there will be more on this on their website). The education element provides guidelines about how to recognise the signs and symptoms of breast cancer, working with women's groups, GPs, nurses etc. The campaigning takes issues effecting breast cancer patients to Parliament, to lobby over issues like better access to drugs, better screening programmes and the length of time patients have to wait between an initial check up finding a lump and diagnosis.
The third is Breast Cancer Campaign. Its activities are similar to Breakthrough's research and campaigning but on a smaller scale. Unlike Breakthrough it does not have its own research centres but scientists can apply for a grant to fund their work at their respective place of study. It holds research meetings bringing the scientists it supports together.
You will find much, much more on the charities' websites, and be able to see which one you think is best suited with the person you are donating on behalf of in mind.
As our scope is somewhat different we work closely together to discuss strategies etc. All three are very worthy causes. Thank you for supporting anyone of them and Merry Christmas. MrsC x