My $.02: I use both, Prawns & Cocktail Shrimp. However, both are not usually my first choice of baits either. Both I fish with a bouyant lure of some kind.
Prawns: I use them usually under heavier river flows, either murky or clearer water. Prawns are tough and stay on the hook with the heavier flows, much tougher than most baits which saves your premium baits for prime times.
Cocktail Shrimp: Use 'em in medium to low flows, unless ya put them in a mesh. I have seen Steelhead chase 'em before as I'm reeling in. I have seen fish and had fish comeback and pick them up several times in a row while I was suffering through missed takes.
It seems good eggs usually will outfish both, C.S. & P. Could just be a confidence factor, etc. too.
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