For bait I use 'Twix' - biscuit with a layer of caramel all chocolate coated - cut a small slice and stick the prongs of the tripper through the caramel layer with the biscuit underneath.

I think that an efficient trap which breaks the neck or smashes the skull is far more humane than any other sort - OK there might be a few seconds of thrashing, but the shock of impact must be fatal every time.