I wouldn't say one is definitely better than the other but do consider the transferrable skills. If you don't explicitly need either (which it sounds like you wouldn't) then don't base it too much around that.
Psychology is a more academic subject and is therefore often favourable. However, it has an element of similarity/overlap with Sociology which means that Drama adds more variety to your options. The confidence and public speaking of drama would be beneficial, but so would the social/personal understanding of Psychology, which puts that fairly equal, to my view.
I'd recommend checking the university websites for your course. See what they prefer, if anything, and if there's anything they don't accept (very rare, to my knowledge, and usually only General Studies). Talk to teachers and form tutors/ head of sixth form. Good luck, and don't stress over it too much!