Which tube size to prefer if several options apply? I have 40-622 (a.k.a. 28x1.5") tires, and Schwalbe offers 
two different sizes of tubes - their models "17" and "19" - as applicable for that tire size.

Ok, either one would surely fit well. But apart from weight difference (150 vs. 220 grams), is there any reason to prefer one over another? Is it better to have as small &amp; light tube as possible? Or perhaps a bit larger and heavier one would be more durable, as it wouldn't be stretched as much? Err on which side?
Basically, the tube box will list the sizes it covers. Make sure your size is within those parameters (and ideally not "on the edge"). Beyond that you'd generally pick the lighter tube for road and the heavier one for off-road.  And a heavier tube will generally provide a slight improvement in puncture resistance.

Avoid very light tubes unless you're a racer, as they will often "leak down" much faster than heavier tubes, requiring you to inflate your tires twice daily in some cases.  (It would be nice if manufacturers rated their tubes based on leakage.)