We have been using cord connected d/w and disposals since it became a requirement to either have a means of disc. for these or a breaker lock if hard wired,it works out better since if the plumber is late we still get our final with a single receptacle.Just a hint if you go the cord connected route mount the box horizontal on the bottom plate of the wall that way is the d/w is installed you can still plug it in without removing it.
Cords are certainly the way to go. I usually put the receptacle under the sink. Some of the high end dishwashers don't allow much room behind them for a cord to plug in and if the plumber gets there before me he doesn't have to wait for the receptacle to be installed. A few dishwashers come with factory cords installed which is a nice bonus.
I like to put a switch in the sink cabinet next door to the dishwasher and I label it dishwasher with my sharpie. It saves me from the cost of the pigtail. the load side of the switch is hardwired into the dishwasher. with both doors open you have a direct line of site from the motor to the disconect means