I throw my opinion in the ring -

30- 40 lb maxima ultragreen leader, double 4/0 hooks tied solid. My experience with slip ties is that they eventually loosen up a little and end up scrunching your herring up in a clump. Solid ties work great with cut plug herring as well as whole herring. To get a great roll and a long-lasting bait out of a whole herring rig as follows: Run both hooks one after the other completely up through and completely out the same hole so they come out the top of the herring's head between it's eyes; take the lead hook and hook it through the top of the herring's back just ahead or right where his dorsal fin is; take the trailing hook and run it clear through the herring just above his vent and let it trail out the other side; take the line running up through it's head and throw a half-hitch around his nose right in front of his eyes; snug it up throwing a kink in his nose giving you your roll. Experiment with how big a bite of his nose you get to obtain the easy roll or fast spin you're after. This way of rigging whole works great and the bait lasts much longer than when the belly cavity tears out of a cut-plug.