I use 6' of 16-20# test mono with poppers and a three section leader for streamers. 40/25/16 #test mono.
You want to keep the leader shorter than the rod. That way the line/leader connection is one less thing to worry about when landing a fish.
As for sharks...
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In this picture, I'm high-stick dead drifting a pair of streamers in the long shore current.
Not something you could do with a sinking line.