.38 Special. Easy to reload. Brass retention is 100%. There have been years when I've bought no .38 Special commercial ammo at all.
.45 ACP. Nice big case, easy to reload. The only way I can afford to shoot .45 regularly ($4/50 for bullets, vs ~$15 for loaded ammo). Brass retention is the problem, of course.
.357 Magnum sometimes.
.380 rarely. I rarely shoot that gun anymore.
If I had something exotic, say, .455 Webley, I would certainly reload for it.