Warwick's math (and stat and OR) school is a very good one too, if not better than the econ one. Actually (from academic sense), Warwick is way ahead of Edinburgh in all of Mathematics, Statistics, Economics and Finance. and also the same for business school reputation (in EU, UK and UK related region).
for OP's case, for sure the first one to be out is the St. Andrews one (which is prestigious school in view of local, but it's not really heard of outside, and also for academic reason).
After that, it really depends on the academics interest and career goal and personal plan, since the major is different.
Econ, Finance, Math and Stat, Business School: Warwick >> Edinburgh
Local Reputation in Private Sector: Warwick >> Edinburgh
Reputation back at China: quite the reverse, most likely due to QS ranking and the name of the city.
p.S. if you are talking about msc in fin math, warwick is definitly within UK top 5.