what do you think of a 38?
Regardless, however, of impact energy, shot placement counts, too.
If you find the .38 more comfortable to shoot and can put it in a half dollar sized spot with good consistency from 15 to 25 feet (which is normal gunfight range), and can get a second shot on target rapidly or engage multiple targets in rapid succession with similar accuracy, you are part way to where you need to be defensively.
Most of the rest is mental. (Situational awareness, avoiding problems by seeing them coming and getting out of the situation before it becomes critical, and being willing to shoot without hesitation when you need to).
Some of it is practice and tactical development (movement, concealment, cover, developing muscle memory to draw your weapon and fire on target--because if you have to think about it once you reach the 'go' point, you may be too late.)
That all said, a .38 on target is better than a .45 that goes wide. Since you are best off practicing with the pistol you'll carry, and the loads you will have in it, .38 ammo has a small advantage in being relatively cheap, too.
Generally, I'd consider using the hardest-hitting round you can comfortably and accurately shoot, but even a .25 auto is better than nothing.