In recent years I've used Universal 61, MAFAC Competition, Weinmann 999.
During the 1960s and 70s Universal made cheaper versions of their centerpulls with similar design features to their 61s. Some had steel levers. So far I haven't need to replace anything but brake pads on the Universals 61s. Weinmann was a Schwinn mainstay for many years, so there are lots of parts around, and lots of cheap bikes with useable bits and pieces of Weinmann brakes. MAFAC is a big topic with a wide selection from good to poor. Peugeot et al French bikes used MAFACs, so I'm sure certain regions have pockets of spare parts.
I find MAFACs have adequate stopping power now that I've replaced the pads with pink and black striped "LaVipere", but it can take strong hands to stop in a panic. The pivot points on the levers seem to wear out quickly, causing sloppiness in the lever. The caliper arms are a little flexible. The springs are a little weak. Finish varies from good to poor.
The Weinmanns stop a little better. I find the lever hoods more comfy. The lever pivot points wear with time, but there are still replacement bits around (they sold trillions of these levers). The caliper arms are quite rigid, and the pivot bolts are sturdy. The springs are moderately strong. Consistently good finish.
The Universals seem to have the best stopping power. These levers are very comfortable, but the aluminum body has a reputation for failure. I've only seen two break, both after hard crashes. The caliper arms are stiff, the pivot bolts are well made, and the springs are quite strong. Consistently good to very good finish.
I haven't used the DiaCompes in twenty years, so I cannot comment on their performance.
Aldo Ross
Monroe, Ohio