General quality of ingredients is higher for Shake Shack than Five Guys so you pay for that. They have good specials, their fries are always nice and crispy on the outside, and they serve beer/wine.
If you're looking to make a quad stack burger, you're better off with Five Guys. If you're looking for a higher quality then I'd go with Shake Shack. Either way, they're fast food burgers, just slightly higher end.
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