That's up to you. Use jumbo, medium or large shrimp, as you prefer, bearing in mind the larger ones will take an extra minute or so to cook through. If you have tail-on shrimp, just pull off the tails before you make shrimp linguine, since they are going to be mixed in and you don't want anyone to accidentally get one in their mouth. Get the fresh or thawed shrimp peeled and deveined before starting on the sauce.