I have lived in the area for 30 years but amazingly have never been to either Cafe San Pietro or Positano. I've been to two other Italian places in Ardmore though. I would recommend Primavera Pizza Kitchen for pizza/Italian food, though it is a little on the expensive side. They have a very nice bi-level space and the food is pleasing if nothing amazing. They have large tables for groups upstairs.
The other place we've been to s Fellini BYOB...both times I went the service was extremely slow, which is the reason I never return there.
I wish there were a better choice for Italian in the Ardmore area but if there is I have not found it. I actually often head up to Bertucci's (gasp!) a so not-chow-ish place, for reliable Italian food at moderate prices.