It all depends on how much you're willing to invest up front, and how many rounds you want/need to reload per hour. The Dillon is more expensive (press, parts and accessories) but more productive. The turret (and by this I mean an auto-indexing turret) is less expensive (can be 1/3rd the cost) but only about 60% as productive as the Dillon 550B. This is in reference to pistol rounds loaded in full progressive or auto-indexed mode.
For rifle rounds, depending on your loading process, the 550 and turret will load the same volume/hr. This is because most rifle loading processes combine on-press and off-press steps which causes either press to be operated like a single stage.
That said, a single-stage offers some advantages for accuracy-oriented rifle loading and is a press that can be used for many special purposes (decapping, bullet pulling, swaging, etc.) that can make it a long-term addition to your bench. A great combination is a single-stage for rifle and a progressive for pistol.
Unless you are a committed reloader, do you know that you will be using the press enough to get your investment out of it? Many prospective reloaders find that they lack time or ongoing interest within a year or two.