The Gillette Slim is much more common than the Fatboy and so generally less expensive, but it shaves as well or better. In fact, many find the lower profile head makes it easier to get right under your nose and in your face's other nooks and crannies. Any of these three would make a great daily driver, and will serve you well for years to come.
Details on the three we currently have available, from left to right in the photos:
The Slim on the far left has an H2 date code, indicating it was produced in the second quarter of 1962. It works great and looks great; it is used but with its plating and painted numbers intact. Really no flaws to speak of with this one.
The middle Slim has an I1 date code, indicating it was produced in the first quarter of 1963. It, too, works great, but does show its age a bit, with a bit of brassing and plating flaws. It retains most of its number paint.
The right-hand Slim has a J4 date code, indicating it was produced in the fourth quarter of 1964. It is almost as nice as the H2, but some of the number paint is gone.