I think s/he is talking about Pokemon Crater, where you can catch normal, shiny or dark pokemon. If we are talking about that, I would say dark because you do 25% more damage.
Sorry if that's not what you were talking about but if you can explain that would be good.
I've only seen 1 shiny in person ever, so I'll have to say regular by default. Besides, I've never understood the obsession with shinies. Just because they're a different color you want them? I think some of the shinies look worse with the different colors, and some look almost the same (look at Skitty's red vs normal pink).
I've never played Pokemon Crater before (if that's what the poll is for), but in all the Pokemon games I like shiny Pokemon the most because they're so rare. <3