Shinies are always more valuable. ALWAYS

Aw now why would you do that? I might've had an extra...

Shinies are generally more valuable, unless it's one of them fancy event legends or something. Though if it's a mascot or something and the shiny isn't too great, that might be worth it. Any trio legendaries are never really worth it; as legends come they're dirt cheap. The swords of justice aren't particularly valuable--they're all available in a full four relatively recent and easily available games.

...well that stinks. I just figured that a Geodude was a pretty common Pokemon I was never going to use, so I might as well get something good in battles instead.

Granted, Terrakion is the most useful swordsmasters

I haven't caught any shinies, but I only catch neat looking Pokemon as a rule, so I'd have a hard time deciding whether or not to catch a shiny of an ugly Pokemon.