Living in Las Vegas, you hear a TON of people wanting to compare Five Guys with In-N-Out. They are both of a higher standard than the normal fast food burger-joint. My opinion?
Burger = Still goes to In-N-Out. That being said, Five Guys has a really tasty (and HUGE) burger. Their standard burger is actually a double-burger. One of my favorite toppings on a burger is grilled onions. I don't know what they do differently, but theirs just don't have the same caramelized... "goodness" that In-N-Out has. That being said, if you order a Bacon burger/cheeseburger you will get a LOT of bacon, and it is crispy and delicious. The burger is a solid 7/10.
And now, the reason you WANT to go to Five Guys...
Fries = Five Guys by a MILE. I "like" In-N-Out's fries. They are a strong 5-6 out of 10 in my book. The burgers are magical, the fries... eh. I've had a LOT better. Five Guys fries are the reason to eat there. Not only are they delicious, but even with a small order, you get a TON of them. They are fresh-cut (yes, I know In-N-Out's are as well, but it's a different cut with a different flavor) and seasoned just right.
The fries will be the reason I go back, and I'll have a pretty-good burger with them while I'm at it.