There is a reason why London is more expensive: it has much more to offer. It's one of the great cities of the world, incredibly diverse and iconic. From what I hear Bristol is a fantastic city, but London is in a league of its own, on par only with NYC, Tokyo, Paris, Berlin and maaaaaybe Mexico City. Depends truly on what you want. I love large, chaotic and complex cities - but then again, that's just me.