I am from Philly originally, and I have to say the best subs are at Alex's Brown Bag in the lobby of the Mr. A's building (5th & Laurel). They are open for lunch, but I think they close early in the evening- 6 or 7 pm. It seems to be the only place with the proper bread. They even have cheez wiz now for properly gooey cheese steaks. Mona Lisa's deli also does some very good subs- and I think both are far better than Grab and Go, where the bread is too soft and meat seems to be lower quality.
In Hillcrest there is a good place on University between 5th and 6th - Capriottis I think. Philly Franks in San Marcos has a good hoagie also - pretty close to what I go home to philly. Apparently Frank imports amoroso rolls which are not the best, but better than most rolls used out here. I've been meaning to try mona lisa's.
Its all about the bread, which seems to be a problem at most places I've tried on the west coast.
TRY THE GRAB N GO FROM GRAB N GO. They are family owned and have several locations in Downtown and one in Kearney Mesa and another one Mission Gorge, near the Hospital.
I also like DeMille's on Adams Ave. They deliver and they are great for dinner, they often have a coupon on their website.
I do not think the Grab N Go's are open past lunch.