Vs. Dragonite which Articuno to power up

Yeah, in this meta, the 15 attack is probably better even though it feels weak to pick a 80% over a 87%. I'm in the same position as you with my 82%/14att being better than my 87%.

I think against dragonite because of the 2X weakness and comparatively low defense (compared to Lugia and Articuno), the breakpoints will not be that critical. Try having a look at the breakpoint spreadsheets to determine if the 12 attack will actually deal less damage than the 15 at your desired level. If it doesn't, then the 15 attack is of no greater benefit.

Correct , the 15 atk 80 percent is the better one , but only by a whole 4cp ...you'd likely not notice a huge difference in the two guys when using them , the 80 percents charge atk might do ~2 more damage , the 87 might last 2 seconds longer

80% because base stats. Being defense covered, i like those 15 atacks even more.