^ The HDs have a stronger spring.

Polymer bases are generally fine. If you're rough on reloads, want the mags to drop faster, the steel are better. They're slimmer, but not shorter, so use with a magwell/concealment are the same.

Mags are consumables, I wouldn't spend extra for a color. The paint isn't as slick as bare stainless and I don't think they're as reliable due to my experience with 'em..