Typically, the safer bet for shrimp is to buy them frozen, as this ensures they are fresh. It’s also easy to thaw and cook them right out of the bag! If you’re feeling adventurous and would rather try fresh shrimp, make sure the shrimp don’t smell like ammonia or have shells that are slimy. They should be firm with solid tails. For a recipe like this one, aiming for medium- to large-sized shrimp is the best option. But your tacos would work with jumbo shrimp. If you want to serve leftover shrimp over rice, mini shrimp would be also delicious for that and would still work as a taco filling (though you might want to take the tail off of them).