The Leica IIIf, produced 1950-1957, is the most common and most recommended Barnack Leica: the refined peak of the screw-mount line before the M3, with over 180,000 made.
It adds flash synchronisation to the IIIc platform - the sync dial beneath the shutter dial gives the Black Dial (1950-52) and Red Dial (1952-57) versions their names - with a cloth shutter 1s-1/1000s on Red Dial bodies, separate finder and rangefinder windows, and the M39 screw mount.
Red Dial examples with the self-timer are the definitive user Barnack: parts and service knowledge remain widely available, and the camera pairs naturally with collapsible Elmar and Summitar lenses of the same era.
Prefer a Red Dial for the 1/1000s top speed and later refinements. Check curtain condition, rangefinder patch, and that the flash sync dial turns freely; a documented CLA adds real value on a camera now seventy years old.