Jupiter-37A
The build as T-34 tank, thick aperture blades that will never stuck even dumped in oil.
I love this lens, from mechanical point of view it's coarse clone of the CZJ Sonnar 135/4, and so it's BETTER than original.
I did not see single one J-37A with mechanical problems, but talking about Sonnar - EACH ONE I've touched was stiff focus ring, or had sticked aperture blades (or both).
Optical quality of J-37A is outstanding, at f3.5 it's maybe slightly soft when compared to Sonnar, but as CZJ product is f4 we can always step down our Jupiter to f4 (sorry, Sonnar).
Well, that's the lens that have had opened my eyes on optical quality of consumer grade Canon zoom lenses.
It's dependalble, rugged friend - I recommend it like no many more lenses.