My PhD is from Madison, and I work now in a department with several colleagues with PhDs from LSE. First of all, congratulations -- those are both top schools. In terms of the quality of education you'll receive at either place, it will be excellent.
In your shoes, though, I'd go with Madison. As great as it is to have someone of Sarah Banet-Weiser's stature interested in your work (and that's fantastic), there's a danger, too, in choosing a school to work with one specific person. I've seen enough people do that only to discover that the match wasn't as good as they thought, but then they're stuck. Not to say that would happen to you, of course, but it's a risk worth considering.
Add to that the question of cost and a job for your spouse. I left Madison pre-Scott Walker and the decimation of public employee unions, including the TAA. We had an excellent TA contract while I was there, and I imagine it's still a good contract, especially because it came with tuition remission. I got through my PhD loan-free, although it helped (a lot!) that my spouse had a job. We even bought a small house (which I miss a great deal). Many of our friends did, too. Not that I'd necessarily recommend it, but I did love that house.
And my spouse had little trouble finding a job in Madison, which is small, but not that small. Dane County has half a million people -- San Francisco it is not, but there were more than a few married students in my cohort, and their spouses all found jobs they liked. (Mine administered federal grants in a state agency.) You didn't mention your spouse's line of work, but Madison has a wide range of industries (tech, non-profit, banking, medical), not to mention the state government -- the opportunities are greater than you might perceive.
London certainly has its appeals, too, but it's not worth going into debt for, especially for a master's program. If you're looking for an academic job, keep in mind the market is very, very hard. I'm the DGS in my department (this is me, if you're curious), and I recommend to all our incoming students to think about what they'll do if an academic job doesn't pan out. (Sorry for being such a downer -- I've just seen a lot of people struggle, and it's hard.) Figuring out Plan B is a lot easier if your debt is limited -- you'll have a lot more freedom.
Plus, to go back to the upsides of Madison, the comm arts department is incredibly strong. The people who teach there now are doing cutting-edge work, and the excitement of working with people pushing the boundaries is contagious -- if you let them, they'll push you, too. Everyone I know has supervised students doing things outside their area of expertise, and from a prof's point of view, that's fun -- students can push us, too. When that happens, as it certainly did for me at the UW, students find ways to become inventive and creative.
So, my two cents worth. Good luck choosing!