I second that intelligence =/= trainability. Intelligence is more so the ability to learn complex tasks, or learn quickly. Trainability is a willingness to obey. Siberian Huskies, in example, are extremely intelligent, constantly learning how to escape or find cold spaces, but they aren't common in obedience rings. Now, with that said, what exactly are you looking for? Working lines are bred to, well, work. They'll go insane without a job, and are very handler-focused, so they're easy to train. However that doesn't mean show lines are dumber than a pile of bricks. They can still learn manners and obedience. It just depends on what type of job you're looking at. In example, a show line would be better for therapy work because they aren't as drivey, but if you want a high level protection dog, a working line would be better because they have the drive and energy for it. That doesn't necessarily mean that the intelligence is different, it's just channeled differently. Working lines are more intense, and show lines are more mellow.
In addition, these are just (typically very accurate) stereotypes. You could find a very mellow working line or an intense show line. VERY unlikely, but point applies.
I noticed you attached a picture of Rin Tin Tin. You should be aware that today's GSD is VERY different from Rin Tin Tin's time. I don't believe then, the lines were segregated at all (?) Or at least not as intensely as today.
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