u/Brickirill

Hi all. So, for my first ever dip into watch repairing, I bought two soviet watches from mid-50s, with identical 2603 movements, one with busted hairspring, the other somewhat running. I did it just to practice most basic skills, but still, it would be nice to build one movement that works.

Now, here's both mainsprings. On the left is the old blued steel one, which looks okay, but I know it can break. On the right, the more modern white alloy spring, which won't break, but looks very worn out.

?So, which one to choose, considering that my goal is not to build for long-term, but to just get the movement running as good as possible without any serious repair work?