While both programs are excellent, we're comparing apples to oranges here. I don't know that much about management programs, but the MSc Finance degree is perhaps the best program LSE has to offer.
An LBS or LSE degree promises a successful career in IB, so either is a great choice. But your choice also depends on what are your specific goals. A management-oriented future would be better served with the LBS degree, while a career with more market, financial, or economic analysis would fit better with LSE. It also depends on your personality. A person blessed with a quantitive mind will probably feel more comfortable in a financial environment.
For me, though, I would choose LSE. Finance is a powerful and versatile tool.
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