In terms of large, North American fast food chains, I like A&W, Carl's Jr/Hardy's, and Jack in the Box. In terms of smaller, regional chains, I think In-N-Out is leaps and bounds the best (though What-A-Burger is also really good). Outside of North America, I'm a pretty big fan of Mos Burger from Japan. JollyBee from the Philippines is also pretty great, but mostly because they serve spaghetti and I find that amusing.

I think Shake Shack is overrated but worth trying. FiveGuys is meh.

I also firmly believe that smaller burger chains like In-N-Out, Shake Shack, and What-A-Burger are probably more or less equal in terms of quality and what determines which you think is best is where you grew up.