Unfunded PhD position or advanced MSc course?

I have been offered an unfunded PhD position in theoretical physics from one of my top PhD course choices. I have also been offered a place on the QFFF course at Imperial, which is a highly regarded and more advanced MSc compared to most. I would be using this second MSc to go on to do a PhD, as I think it would open PhD opportunities I didn't have previously. Neither are ideal, but what is the better option?

Should an unfunded position also be considered as a rejection?