In the long run, IMO common shotguns are your best bet.
Want parts for a common Browning, Beretta or Remington? You can have them ordered in five minutes, sometimes from any of several competing manufacturers and retailers. Custom stock? Youth stock? Pre-fit recoil pad? They're everywhere.
Want parts for an older model from some random brand? Maybe you'll find 'em, maybe you won't. Collectors may enjoy looking for rare parts to fix a unique gun, but for hunting and shooting, that can mean you're without a gun for a while.
Even SKB says "tough ****!" in more polite words on their website, if you want parts for some of their older but often-seen models.
AFAIK CD hasn't actually made anything since our grandfathers were buying their first shotguns. They import guns of various quality from various places. The varied reports in this thread speak to the mixed results.
Depends what you want, really, and what kind of deal you find.