An RN is a career track. This will be frowned upon and will give you an uphill battle for admissions.
A CNA is an OK choice I guess. I know mostly nurses who did that to get their foot in the door. I know the CNAs at my hospital are kept busy with long hours, so it may not be very friendly for a pre-med curriculum.
The best thing you can do for clinical experience is clinical volunteering. Medical school will start you not at step 1, but at step ZERO. All you need is exposure to the clinical environment, so you know what you're getting into. You don't need to learn any specific skills. I had plenty of former EMTs, scribes, etc in my class, and I never felt behind despite never having done stuff like checked blood pressure, pulse, or anything similar prior to starting medical school.