I don't consider In-N-Out to be the second best burger chain in the US (that would be Steak 'n Shake. INO is 3rd. Five Guys is, of course, #1.), but they are the winner in their region. And they have a very loyal and fanatical following. So I eagerly anticipate the Burger Wars that will begin with the large-scale movement of 5G into California.
There are currently just three 5Gs in California. This article in the OC Register mentions they are planning a further 300 locations in the Golden State, and the many of them will start appearing next year. INO only has 232 locations in 4 states, so 300 5G in just California is going to be intense. I've had both burgers, in the same weekend, and I have no doubt the winner will be wrapped in foil and served in a greasy brown bag.