I have preferred Multiwave off in each of the dozen or so times I have compared since getting my P3 years ago. To me, Multiwave sounds less dynamic, with rolled off high end on all of the (solid state) stereos I have connected my P3 to.
There is an old poll in another thread where 40% of us prefer Sine (Multiwave off) - Favorite multi wave level? - #16 by bootzilla