As far as I'm concerned, catching the legend is what counts; not the kind of ball it's in. I'll use whatever is the most effective at the time; Dusk at night, Ultra in general, and then Net balls on water and bug types. Since I don't use legendaries except as great trading fodder for items and Pokemon I need, and since I breed for IVs on every Pokemon I plan to raise competitively, the ball a Pokemon is in upon being caught means nothing to me.