it depends on what you are trying to make. When I made the bungs for my 44 gallon drums I did it doms way with seperate geo and bevel the top of the cube...otherwise its difficult as you will edge loop to get it to smooth well but this will deform the overall shape of the dish if Im correct.

cheers bullet

this was done doms way...seperate geo..bevelled the top 2 edges on the cube the smoothed all.