In my opinion, I would say that you should do whichever you are more interested in. If you aren't interested in something, you aren't going to put the most effort into it. Do ECs that you really enjoy and it will really show, especially during interviews.
It also depends on the kind of schools you want to go to. If you want to go to a school thats heavy in research, you will likely need research experience to get considered.
You must have clinical experience to be considered. Research experience is desirable because more schools will look at you, but is not required. If you already have lots of clinical exposure, then do the research.