I'm coming to the conversation pretty late but here goes. I originally signed up with Swiss Medical on a cheapish monthly plan (500 pe') late 2012 and at first found the quality lacking because only the Swiss Medical clinics were part of the plan and I had really lousy service the few times I had to go (as soon as you sit down they're in a rush to push you out the door with a prescription but no further advice). When I could finally be included in my boyfriend's 'family group' after getting a certificado de convivencia from the CGPC, I moved up to a better plan still with Swiss/Docthos and started using more services.
What I learned from this experience is that you have to shop around, ask friends for recommendations and keep going until you find good medical professionals you feel comfortable with. In the last year before leaving Argentina, once I got the hang of the system, I used the health plan more than ever, getting my teeth cleaned, my foot operated on, orthopaedic insoles, reading glasses, you name it.
@Big Al, I don't think they generally speak English at SM, but there may be one or two customer service reps who could comfortably assist you in English. You could always go to the branch nearest you (Santa Fé 3700?) and ask. You could start with "Me gustaría afiliarme a una prepaga (prepaid insurance), hay alguien acá que habla inglés? That way they can point you in the right direction.
Good luck!