They're different. For those of us who prefer traditional, Colt-style half cock lockwork, they are better. Then there are those who prefer the safety of the New Models.
The guns that are referred to as "three screws" are what Ruger calls "Old Models". Those are all their single action revolvers built before 1973 when Ruger completely redesigned the lockwork to what it is today. The term "three screw" comes from the presence of three big slotted head screws in the side of the frame like a Colt. These screws are the pins that the hammer, trigger and bolt pivot on. New Models have two headless pins, rather than screws. The trigger and bolt pivot on the same pin. Believe it or not, that's the short version.
Good luck finding an affordable .45Colt Old Model. They actually produced fewer of these than the infamous .357 and .44 flat-top models (1955-1962) and they command a premium. Only built for two years, right at the end of Old Model production. Expect to pay at least $500 for a well-used shooter grade sixgun.
What people refer to as flat-tops are those "Old Model" .357 and .44 Blackhawks produced from 1955-1962 for the .357 and 1956-1962 for the .44. These have a completely flat topstrap, reminiscent of the old Colt flat-top target model, with a steel Micro adjustable rear sight. In 1962 they added the protective ears around the rear sight and changed the sight itself to a proprietary aluminum model. Old Model Single Sixes with drift adjustable rear sights are not flat-tops. There are other differences but this will cover the basics.
Note the three screws in the side of the frame on this flat-top.
Note the two headless pins in the same general location on this New Model.
