def slotted over cross drilled or both !
drilled rotors reduce the surface and actually reduce heat dissipation since there is less metal (for conduction - robmarch is correct - back in the day they were made to let the gasses escape) ...
in the end tho any of these are overkill for the alty on street duty, so greensoup is right in that sense..
however, i dunno what its like for you boys up there, but the OEM charge for new rotors here is pretty pricey, and its really a matter of a few bucks to get a quailty set of ventialted and slotted brembos... i really cant see the objection in that.