Who's sp3 impressed you the most the first time?
For me it was Scarlet Witch. The first time I got hit with it I was thinking only of how majestic it was even as my health was going down. I was even tempted to push her to sp3 just to see it again. Later when I got her as a 4*, I spammed that sp3 like there's no tomorrow. I took her, unawakened in every quest just so I could see that sp3 one more time.
The only other champions whose sp3 have impressed me like that are Doom, Ronin and recently, Airwalker.