If you talk to most people in the San Fernando Valley, the answer they will likely come up with is Brent's Deli. Brent's is great with an amazing menu and two large restaurants ready to greet your family. They are also the valley's favorite deli for catering. Another great choice is both Weiler's Delis in the West Valley. While they have different owners, both provide a consistently great deli experience.
Once you leave the Valley, there is no clear winner on the deli front. Many people love Cantor's Deli in the Fairfax area.
Factor's Delis is also a popular deli in Pico.
Langer's Deli is another great choice of delis.