Re: which caliber for all around use?
.410's aren't the greatest shell for autoloaders or pumps for certain. new commercial rouns will feed, sure, but like ya say some loads or old tired reloads won't hold up in anything but a fixed barrel, either single or double. 12g hulls last longer and have so many more options of projectiles and of course power. 1/5oz slugs are usually moving around 1800fps though in the little .410, so velocity isn't really much different between .410 and 12. just the payload.
barrel length has absolutely nothing to do with choke/pattern. The choke merely 'grabs' onto the wad moreso and allows the shot to leave the barrel less molested resulting in tighter patterns. whether that's at the end of an 18" barrel or a 28" barrel makes no difference.
and yes, on full choke for the .410 being about the only option, not enough shot to fill a larger pattern and be effective.
"Loud noises don't end gunfights.... well placed shots do."