Internship advice needed

I'm having a bit of an internship dilemma and was hoping the lovely people of the student room could offer some advice.Heres my situation; I am a second year science student who did a science-related internship last summer, but I'm not really sure if that is what I want to do after uni, so this year I decided to apply for internships in different proffesions.I have an internship offer from Deloitte, who need to know my decision by Monday.I also have an assesment centre for a legal vacation scheme next week and if I were to be offered a place (unlikely I know, but hey, a girl can dream) the dates do not clash with Deloitte so I would be able to do both.I had also applied to RBS, but hadn't heard from them for 3 weeks so assumed I hadn't been sucessful, but then yesterday they invited to an assesment day. This internship would take up my whole summer and would mean I would have to reject Deloitte, and also the law firm if I got it.Initially I thought I would withdraw my RBS application (and let someone else have my place at the assesment day) and accept Deloitte; best case scenario being that I also get the legal vac scheme and will get an insight into two non-science related professions, worse case scenario being I have Deloitte and will use the two weeks of the vac scheme to go travelling.However, now I'm having second thoughts becasue I know many people put IB placements as their first choice over big four, so would I be silly to reject the opportunity of an IB internship? On the other hand would I be foolish to reject my Deloitte offer in favour of just the possibility of an offer from RBS?Also, if I withdraw my RBS application, is this likely to burn bridges with RBS and reduce my chances of getting graduate job with them (or any IB for that metter) if I decide I would like to persue a career in IB afterall?