i use both, i have several dillion square deal presses in 45, 9mm,38/357,40 cal.
and lee turret that i use for calibers i don't shoot as much, 45 colt, 44 mag, 44 special, 44-40, 32 mag.38 super and several others. they alow you to produce a lot of ammo in a short time.
i also still use a rcbs rockchucker press for several rifle calibers, and i assemble carry ammo on the single stage press so i can check each powder charge. if you are going to load you need both, but you could just buy a dillion 550b with conversion sets, but i don't like to spend time converting the press.