Which is the best area -- accounting OR finance for a student who is already pursuing ACCA & is very likely to work in investment banking?

If you refer investment bank as traders, then nope. These jacks only recruits from target elite schools, such as Oxbridge, LBS, LSE, ICL, UCL in the UK, Ivy league level schools in the US, If you mean analyst jobs, then an accountant qualification can break into, but it's more geography relevance, t