It all depends on the hospital. As a rule of thumb, if you are a CNA, you are eligible to be a PCT in most hospitals. Doesnt mean you would get hired, but that is usually a cert that would be good for any hospital that has a minimum certification requirement. At the hospital I work at its required for all PCTs. EMT and other certs might also help, but you still need to be a CNA.
Other hospitals require you be at least one of the above. EMT, CNA, MA, or have one semester of RN school. For these hospitals EMT would make you minimally qualified and eligible for the job. Having worked as a PCT and being an EMT, I would say that of those certs, EMT would be the LEAST qualified for a PCT job, because pre hospital EMS has little in common with an inpatient or long term setting. That doesnt mean you couldnt get hired in as an EMT, only that it would be less likely, and you would have a steeper learning curve than the others.
Techs who work in the ER are often EMTs, but everyone and their sister wants to be an ER tech, so those jobs are extremely hard to get and they usually require previous experience.