A good hook for fly fishing will ideally be a good match to your fly - strong enough for whatever you might be hoping to hook up to but light enough not to compromise the tracking of whatever you've tied up.
While you’ll generally use hooks between 1 and size 5/0 for saltwater fly fishing, there is no one-size-fits-all regarding hooks. You have to select your hook based on several factors, including the size and weight of the fly and the type of fish you are fishing for.
Flats flies like those used for bonefish are typically size 2-8
Flies for striped bass are typically tied on size 2-3/0
Call if you have questions about hook selection.