Bunny leech is easier to tie (marginally so), and uses fewer materials (just 1). You can also wrap the entire shank with as much lead as you want, versus a slumpie that would look like a fat person in a tiny jacket if you did that.
I, personally, think a bunny leech looks better in the water and draws more aggression strikes. Slumpies have the bright underside to imitate sculpins. These fish care not about sculpins.
http://www.riverbum.com/Bunny-Leech-White/
Tie in the tail, "palmer" the body, admire. Cross-cut strips work best for the body, but are not even remotely necessary.
More evidence for my color theory:
I'd toss a dark blue bunny leech and move a fish. 10 minutes later, nothing. Toss a baby blue, move a fish. 10 minutes later, nothing. Toss a purple leech, move a fish. Etc.
I'll add that I much prefer slumpies for trout.
Bring your steelhead flies too. They will be in, as will the browns. I have had the most success with flesh flies during the run. Get yourself some flesh colored (off-white, occasionally pinkish) bunny for that and get creative.