There are a number of criteria with which you could compare Fatburger to In-N-Out. For example, you could compare the appearance of the restaurants- Fatburger has a pretty normal fast food restaurant vibe, whereas In-N-Out has that weird thing they do where every restaurant looks exactly the same and kind of gives me the willies. Or you could compare the variety of the two menus- Fatburger offers fried chicken with buffalo sauce, turkeyburgers, veggieburgers, and breakfast burgers, and In-N-Out offers burgers only (yeah you can get "grilled cheese" off of the "secret menu" but that hardly counts). There are also the fries- Fatburger has fat or skinny fries, and you can get chili on them! In-N-Out has those dry, starchy and flavorless fries. Finally, you might consider celebrity endorsements- Fatburger has Ice Cube, and In-N-Out throws its lot in with Jesus. In any of the above categories, I'd pick Fatburger over In-N-Out. But this comparison was about the burgers, and in the end, I'd say In-N-Out can't be beat in that category. Still, either restaurant is a good choice if you are short on time and money and want a cheeseburger.
part 1 - fatburger
part 2 - in-n-out