This is all dependent on aircraft as well. You have an Optimized profile, a Crossing profit, and then there is a normal or comfortable profile (I made all of those up). I think most of anything other than RJ's use an ODP for an Idle descent. In the CRJ for example it's not really practical to do this when you have step down fixes and other things like tail winds. Idle decent in a CRJ holding a anything over 300KIAS is pretty aggressive and not comfortable for passengers. At least that has been my experience. Seems like rule of thumb is to descend at 3 degrees and it works well. Except for those short stepdowns and such.