Which one of these has a better reputation for a finance degree?

I think both are very strong. Cass is right there in the City of London - the banking and finance center of town. Imperial also has a nice roster of finance electives, and at least two specialized MSc programs in finance.

Reputation wise both are very comparable. They are pretty close to each other in the most recent global full-time MBA rankings in the FT ... Cass (#32) and Imperial (#37).

Good luck!