Self-Study
I'd recommend self-study, because that's the way I did it and I passed. Its also cheaper to buy/borrow the books and sacrifice spare-time to actually read the books and answer the questions in the PPL confuser.
However, a friend of mine learnt the PPL groundschool subjects on a full-time course in Bournemouth, and doesn't regret paying the money for it. He got first-time passes and better scores than I did, and in less time.
What option you choose really boils down to what your licence is for you. Is it important that you know the subject matter really well, and are you looking to flying for a career in the airlines? Or do you just need to know enough to be safe in the air, and just want to fly for fun? If its the latter, maybe a full-time groundschool course would actually be wasting money that could be better spent on flying hours.