Apart from anything else, it's not really easy for us to tell what your responsibilities would be for each of the first two job titles. In one organisation, someone with 'administrator' as their job title might spend their entire day entering data into spreadsheets, whereas an 'administrator' in a different organisation might have quite a lot of responsibility for, say, deciding who gets priority on a housing list.
Similarly, some 'customer service executives' might do nothing other than call centre work, whereas others might have to handle irate customers who've got complaints about goods or services.
So, without seeing the full job descriptions, it's hard for us to know which jobs might be best for you.
Even the 'dental receptionist' role isn't one that's necessarily clear cut. In a big practice, the receptionist might simply take bookings and welcome patients, while hardly ever needing to set foot inside an actual dental surgery. In a one-man (or one-woman) practice though, a 'dental receptionist' might spend much of their time working directly alongside the dentist.
If you were lucky enough to be offered all three roles, go for the one where (based upon what you learn at the interviews) you think that you'll feel the most confident and relaxed in your work.