as someone who worked both and an EMT and a CNA, I can say that I have seen more pre-med emts than cnas (I know of two other premed cnas).
EMT-basics (which correct me if I'm wrong, is what we're taking about here) are over-glorified taxi drivers to some poeple, getting an intermediate or medic gives you much more autonomy, and greater scope of practice as to what drugs you can push (this is where the fun starts), but all this changes from state to state. And it takes at least two years to reach these level in most states.
however as a cna (especially night shift, which I work, so of course I'm biased), gives you the chance to read charts, look at in depth medical histories, look up drugs, doses, what tests are ordered, what the labs are, and lots of vocabulary in Tabers.