My gut feeling is that there are pros and cons to both.
As with any "sub-specialty" technician position, adcoms won't see them often and will thus make your application stand out. Personally I am an ophthalmic tech, which is apparently quite unusual within the pre-med population. All the people I interviewed with commented on that experience in particular, with most stating they had never before met someone who was an ophthalmic tech. I imagine it is probably the same with a sleep tech. HOWEVER, I think the deciding factor for determining whether a position is a valuable clinical EC is exposure to and working with physicians. Everyone asked whether I had the opportunity to see what a physician does. They seemed less interested in my direct patient care experience.
I have the unique perspective of also having worked as an ER scribe for a year. BTW, this experience was NEVER mentioned by any of my interviewers. I was always the one to bring it up, and most just responded as "yeah thats cool, lets go back to talking about your ophthalmic tech experience." There is however one huge advantage to ER scribing; you are guaranteed to work closely with physicians, and you get to learn and see A LOT! The big drawback is that nowadays, I feel that many applicants have worked as an ER scribe. I met several other applicants on the interview trail who had also been a scribe. Therefore you will be just one of the many applicants with that on your application.
Of course take this with a grain of salt. All schools are different and the application process is such a crapshoot. As people always like to say, this is anecdotal evidence where n=1, and thus a piss poor sampling size.
