There are a few recent threads on this. It might be worth doing a search.
BGS are generally recommended the most, along with Oxford. There are others e.g. CATS which are cheaper. I'm using CATS but with BGS notes (bought second hand) which is working quite well for me so far. Others seem to be finding the CATS notes okay, but I prefer the BGS ones personally. Horses for courses!
CATS also split the course into three segments which allows you to attend three 1 week brushups, rather than the two 2 week sessions BGS require. That works better for me with work commitments.