Suggestion:
Accounting would be the better of the two, but you'll need to take classes in all the business disciplines in order to succeed in investment banking. Having said that, I did econ as an undergrad and also did investment banking, but that was after an MBA. If you want to try investment banking straight out of undergrad as an Analyst in corporate finance, I would do a BBA in finance or accounting being sure to take coursework in marketing, strategy, econ and all the other business disciplines in addition to your major.
I would also suggest a MBA rather than a masters in finance if you want to pursue investment banking. A masters in finance will carry more weight in academic circles or very technical financial careers. An MBA will appeal more to employers that need multidisciplinary talent for jobs like investment banking.
Good luck!
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Definitely do accounting. I double-majored in finance and economics as an undergrad. Now I'm looking for work, and I'm not even qualified for many interesting positions because I don't have enough accounting coursework. Accounting will make you more competitive for the workforce in case you decide to not to go to graduate school immediately after getting your bachelor's degree.
In my opinion, a good knowledge of accounting will help you when you take up your Master's. This is because Accounting is more practical and you will be encountering problems in Finance which will require basics of accounting whereas Economics is a theory based subject and you will be working extensively on models and theories which would not have a direct application in Finance.
Go for accounting as you intend to do a master in finance and go for a career in investment banking.
Best wishes