Don't take me wrong. I, myself, think of LSE as a fine institution. It is excellent for Law, Economics, Politics, IR... But from what I gathered, the OP is looking for a broad general philosophy degree, rather than one specialised in philosophy of science (if I am wrong, please correct me. I would strongly recommend LSE if Philosophy of Science is what you are after). I also speak from personal experience. I considered applying to LSE for masters in philosophy, but was discouraged by my tutor because LSE's philosophy department is so focused on philosophy of science, while I am interested in moral philosophy and philosophy of religion. I have to admit I only considered applying to LSE only because of its general reputation. So let me warn you, don't go/apply to LSE if you are only attracted by its general reputation!
If I were to compare UCL and LSE for philosophy. I would definitely choose UCL over LSE, in fact I applied to UCL for masters too, just in case I don't get into Masters here at Oxford. Again this is assuming philosophy of science is not what you want to specialise in.