This city covers more than 1500 square miles (in LA and Orange Counties). Much of it is commercial and encompasses large enclaves of just about every ethnic group you could think of - with more on the way.
It would take half a lifetime to adequately survey the markets in this city, and by then you'd have to start over because so many would have changed.
I visit a few markets that serve me very well, and add a new one now and then for special items or ethnic cuisines.