All IMHO, but....
White Castle sliders are simply the worst "burgers" ever made. Plain McDonald's hamburgers (the cheapo specials) spank White Castle burgers up and down the block - at least they taste of pickles, weak mustard, mild onions, and a tinge of meat. White Castle tastes like oily bread. That's how bad they are.
In-N-Out gets boring pretty quickly. Even when served animal style, their burger is not exactly exceptional. I'd rather spend a little more for a real diner-style burger, or a Nation's burger. But if any non-Californians ever visit the state, do try In-N-Out at least once, especially if you can't find a Nation's nearby. They're pretty good the first few times you have them.
But really, for late night burgers, look no further than the Sourdough Jack. In fact, I just had one an hour ago. I'd rather hit the JITB at this hour for one of these than make my own patty melt w/bacon & Monterey Jack on buttered sourdough toast. Just make sure to skip the one from Carl's Jr., which isn't anywhere near as good.
To the Californians: You might disagree with me on JITB, but you know Nation's is better than In-N-Out. Come on, you KNOW it. A burger & pie at Nation's or Lori's beats In-N-Out with a stick.