Panini or Sammie joint in SF?
First of all, a Panino just means a sandwich. I do not understand how most of us, Americans, got the idea that a panino was a grilled or pressed sandwich. (I was dispelled of that notion about 4 years ago while in Grad school in Italy.) A pressed or grilled panino is a panino scaldato which means a heated up sandwich. I know Bar Bambino has had complaints from customers that order their delicious mortadalla panino because they expect it to be pressed/grilled simply because it is called a panino which is so wrong, I don't even know where to start.
Now to answer your question, the best italian sandwiches, hot or cold, that I have had in San Francisco are at Bar Bambino. Massimo del Panino in FiDi comes a close second. Other than that, you will get sandwiches that are pressed but that have about 3 ingredients too many to really be considered a sandwich with Italian soul.
Now for great sandwiches in general, I really like La Torta Gorda for Mexican beauties or Saigon Sandwiches for Vietnamese tasty ones.