Going to a uni in London has very little, if ANYTHING, to do with your chances of getting a TC at an MC firm. All unis have law fairs where firms attend to sell themselves to the students. Warwick has an excellent reputation, not only for law but in general, which IMO is superior to that of QM. QM's main positive is its location, and even then that doesn't really give it an edge.
Worth pointing out that QM, whilst being a UoL uni, is one of the weaker London unis...if your choice was UCL or something for example it'd be different. But IMO Warwick has the edge here. Also not biased, don't go to either of these unis.